TOMOYO Linux Cross Reference
Linux/kernel/workqueue.c

   // SPDX-License-Identifier: GPL-2.0-only
   /*
    * kernel/workqueue.c - generic async execution with shared worker pool
    *
    * Copyright (C) 2002           Ingo Molnar
    *
    *   Derived from the taskqueue/keventd code by:
    *     David Woodhouse <dwmw2@infradead.org>
    *     Andrew Morton
   *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
   *     Theodore Ts'o <tytso@mit.edu>
   *
   * Made to use alloc_percpu by Christoph Lameter.
   *
   * Copyright (C) 2010           SUSE Linux Products GmbH
   * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
   *
   * This is the generic async execution mechanism.  Work items as are
   * executed in process context.  The worker pool is shared and
   * automatically managed.  There are two worker pools for each CPU (one for
   * normal work items and the other for high priority ones) and some extra
   * pools for workqueues which are not bound to any specific CPU - the
   * number of these backing pools is dynamic.
   *
   * Please read Documentation/core-api/workqueue.rst for details.
   */
  
  #include <linux/export.h>
  #include <linux/kernel.h>
  #include <linux/sched.h>
  #include <linux/init.h>
  #include <linux/interrupt.h>
  #include <linux/signal.h>
  #include <linux/completion.h>
  #include <linux/workqueue.h>
  #include <linux/slab.h>
  #include <linux/cpu.h>
  #include <linux/notifier.h>
  #include <linux/kthread.h>
  #include <linux/hardirq.h>
  #include <linux/mempolicy.h>
  #include <linux/freezer.h>
  #include <linux/debug_locks.h>
  #include <linux/lockdep.h>
  #include <linux/idr.h>
  #include <linux/jhash.h>
  #include <linux/hashtable.h>
  #include <linux/rculist.h>
  #include <linux/nodemask.h>
  #include <linux/moduleparam.h>
  #include <linux/uaccess.h>
  #include <linux/sched/isolation.h>
  #include <linux/sched/debug.h>
  #include <linux/nmi.h>
  #include <linux/kvm_para.h>
  #include <linux/delay.h>
  #include <linux/irq_work.h>
  
  #include "workqueue_internal.h"
  
  enum worker_pool_flags {
          /*
           * worker_pool flags
           *
           * A bound pool is either associated or disassociated with its CPU.
           * While associated (!DISASSOCIATED), all workers are bound to the
           * CPU and none has %WORKER_UNBOUND set and concurrency management
           * is in effect.
           *
           * While DISASSOCIATED, the cpu may be offline and all workers have
           * %WORKER_UNBOUND set and concurrency management disabled, and may
           * be executing on any CPU.  The pool behaves as an unbound one.
           *
           * Note that DISASSOCIATED should be flipped only while holding
           * wq_pool_attach_mutex to avoid changing binding state while
           * worker_attach_to_pool() is in progress.
           *
           * As there can only be one concurrent BH execution context per CPU, a
           * BH pool is per-CPU and always DISASSOCIATED.
           */
          POOL_BH                 = 1 << 0,       /* is a BH pool */
          POOL_MANAGER_ACTIVE     = 1 << 1,       /* being managed */
          POOL_DISASSOCIATED      = 1 << 2,       /* cpu can't serve workers */
          POOL_BH_DRAINING        = 1 << 3,       /* draining after CPU offline */
  };
  
  enum worker_flags {
          /* worker flags */
          WORKER_DIE              = 1 << 1,       /* die die die */
          WORKER_IDLE             = 1 << 2,       /* is idle */
          WORKER_PREP             = 1 << 3,       /* preparing to run works */
          WORKER_CPU_INTENSIVE    = 1 << 6,       /* cpu intensive */
          WORKER_UNBOUND          = 1 << 7,       /* worker is unbound */
          WORKER_REBOUND          = 1 << 8,       /* worker was rebound */
  
          WORKER_NOT_RUNNING      = WORKER_PREP | WORKER_CPU_INTENSIVE |
                                    WORKER_UNBOUND | WORKER_REBOUND,
  };
  
 enum work_cancel_flags {
         WORK_CANCEL_DELAYED     = 1 << 0,       /* canceling a delayed_work */
         WORK_CANCEL_DISABLE     = 1 << 1,       /* canceling to disable */
 };
 
 enum wq_internal_consts {
         NR_STD_WORKER_POOLS     = 2,            /* # standard pools per cpu */
 
         UNBOUND_POOL_HASH_ORDER = 6,            /* hashed by pool->attrs */
         BUSY_WORKER_HASH_ORDER  = 6,            /* 64 pointers */
 
         MAX_IDLE_WORKERS_RATIO  = 4,            /* 1/4 of busy can be idle */
         IDLE_WORKER_TIMEOUT     = 300 * HZ,     /* keep idle ones for 5 mins */
 
         MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
                                                 /* call for help after 10ms
                                                    (min two ticks) */
         MAYDAY_INTERVAL         = HZ / 10,      /* and then every 100ms */
         CREATE_COOLDOWN         = HZ,           /* time to breath after fail */
 
         /*
          * Rescue workers are used only on emergencies and shared by
          * all cpus.  Give MIN_NICE.
          */
         RESCUER_NICE_LEVEL      = MIN_NICE,
         HIGHPRI_NICE_LEVEL      = MIN_NICE,
 
         WQ_NAME_LEN             = 32,
         WORKER_ID_LEN           = 10 + WQ_NAME_LEN, /* "kworker/R-" + WQ_NAME_LEN */
 };
 
 /*
  * We don't want to trap softirq for too long. See MAX_SOFTIRQ_TIME and
  * MAX_SOFTIRQ_RESTART in kernel/softirq.c. These are macros because
  * msecs_to_jiffies() can't be an initializer.
  */
 #define BH_WORKER_JIFFIES       msecs_to_jiffies(2)
 #define BH_WORKER_RESTARTS      10
 
 /*
  * Structure fields follow one of the following exclusion rules.
  *
  * I: Modifiable by initialization/destruction paths and read-only for
  *    everyone else.
  *
  * P: Preemption protected.  Disabling preemption is enough and should
  *    only be modified and accessed from the local cpu.
  *
  * L: pool->lock protected.  Access with pool->lock held.
  *
  * LN: pool->lock and wq_node_nr_active->lock protected for writes. Either for
  *     reads.
  *
  * K: Only modified by worker while holding pool->lock. Can be safely read by
  *    self, while holding pool->lock or from IRQ context if %current is the
  *    kworker.
  *
  * S: Only modified by worker self.
  *
  * A: wq_pool_attach_mutex protected.
  *
  * PL: wq_pool_mutex protected.
  *
  * PR: wq_pool_mutex protected for writes.  RCU protected for reads.
  *
  * PW: wq_pool_mutex and wq->mutex protected for writes.  Either for reads.
  *
  * PWR: wq_pool_mutex and wq->mutex protected for writes.  Either or
  *      RCU for reads.
  *
  * WQ: wq->mutex protected.
  *
  * WR: wq->mutex protected for writes.  RCU protected for reads.
  *
  * WO: wq->mutex protected for writes. Updated with WRITE_ONCE() and can be read
  *     with READ_ONCE() without locking.
  *
  * MD: wq_mayday_lock protected.
  *
  * WD: Used internally by the watchdog.
  */
 
 /* struct worker is defined in workqueue_internal.h */
 
 struct worker_pool {
         raw_spinlock_t          lock;           /* the pool lock */
         int                     cpu;            /* I: the associated cpu */
         int                     node;           /* I: the associated node ID */
         int                     id;             /* I: pool ID */
         unsigned int            flags;          /* L: flags */
 
         unsigned long           watchdog_ts;    /* L: watchdog timestamp */
         bool                    cpu_stall;      /* WD: stalled cpu bound pool */
 
         /*
          * The counter is incremented in a process context on the associated CPU
          * w/ preemption disabled, and decremented or reset in the same context
          * but w/ pool->lock held. The readers grab pool->lock and are
          * guaranteed to see if the counter reached zero.
          */
         int                     nr_running;
 
         struct list_head        worklist;       /* L: list of pending works */
 
         int                     nr_workers;     /* L: total number of workers */
         int                     nr_idle;        /* L: currently idle workers */
 
         struct list_head        idle_list;      /* L: list of idle workers */
         struct timer_list       idle_timer;     /* L: worker idle timeout */
         struct work_struct      idle_cull_work; /* L: worker idle cleanup */
 
         struct timer_list       mayday_timer;     /* L: SOS timer for workers */
 
         /* a workers is either on busy_hash or idle_list, or the manager */
         DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
                                                 /* L: hash of busy workers */
 
         struct worker           *manager;       /* L: purely informational */
         struct list_head        workers;        /* A: attached workers */
 
         struct ida              worker_ida;     /* worker IDs for task name */
 
         struct workqueue_attrs  *attrs;         /* I: worker attributes */
         struct hlist_node       hash_node;      /* PL: unbound_pool_hash node */
         int                     refcnt;         /* PL: refcnt for unbound pools */
 
         /*
          * Destruction of pool is RCU protected to allow dereferences
          * from get_work_pool().
          */
         struct rcu_head         rcu;
 };
 
 /*
  * Per-pool_workqueue statistics. These can be monitored using
  * tools/workqueue/wq_monitor.py.
  */
 enum pool_workqueue_stats {
         PWQ_STAT_STARTED,       /* work items started execution */
         PWQ_STAT_COMPLETED,     /* work items completed execution */
         PWQ_STAT_CPU_TIME,      /* total CPU time consumed */
         PWQ_STAT_CPU_INTENSIVE, /* wq_cpu_intensive_thresh_us violations */
         PWQ_STAT_CM_WAKEUP,     /* concurrency-management worker wakeups */
         PWQ_STAT_REPATRIATED,   /* unbound workers brought back into scope */
         PWQ_STAT_MAYDAY,        /* maydays to rescuer */
         PWQ_STAT_RESCUED,       /* linked work items executed by rescuer */
 
         PWQ_NR_STATS,
 };
 
 /*
  * The per-pool workqueue.  While queued, bits below WORK_PWQ_SHIFT
  * of work_struct->data are used for flags and the remaining high bits
  * point to the pwq; thus, pwqs need to be aligned at two's power of the
  * number of flag bits.
  */
 struct pool_workqueue {
         struct worker_pool      *pool;          /* I: the associated pool */
         struct workqueue_struct *wq;            /* I: the owning workqueue */
         int                     work_color;     /* L: current color */
         int                     flush_color;    /* L: flushing color */
         int                     refcnt;         /* L: reference count */
         int                     nr_in_flight[WORK_NR_COLORS];
                                                 /* L: nr of in_flight works */
         bool                    plugged;        /* L: execution suspended */
 
         /*
          * nr_active management and WORK_STRUCT_INACTIVE:
          *
          * When pwq->nr_active >= max_active, new work item is queued to
          * pwq->inactive_works instead of pool->worklist and marked with
          * WORK_STRUCT_INACTIVE.
          *
          * All work items marked with WORK_STRUCT_INACTIVE do not participate in
          * nr_active and all work items in pwq->inactive_works are marked with
          * WORK_STRUCT_INACTIVE. But not all WORK_STRUCT_INACTIVE work items are
          * in pwq->inactive_works. Some of them are ready to run in
          * pool->worklist or worker->scheduled. Those work itmes are only struct
          * wq_barrier which is used for flush_work() and should not participate
          * in nr_active. For non-barrier work item, it is marked with
          * WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works.
          */
         int                     nr_active;      /* L: nr of active works */
         struct list_head        inactive_works; /* L: inactive works */
         struct list_head        pending_node;   /* LN: node on wq_node_nr_active->pending_pwqs */
         struct list_head        pwqs_node;      /* WR: node on wq->pwqs */
         struct list_head        mayday_node;    /* MD: node on wq->maydays */
 
         u64                     stats[PWQ_NR_STATS];
 
         /*
          * Release of unbound pwq is punted to a kthread_worker. See put_pwq()
          * and pwq_release_workfn() for details. pool_workqueue itself is also
          * RCU protected so that the first pwq can be determined without
          * grabbing wq->mutex.
          */
         struct kthread_work     release_work;
         struct rcu_head         rcu;
 } __aligned(1 << WORK_STRUCT_PWQ_SHIFT);
 
 /*
  * Structure used to wait for workqueue flush.
  */
 struct wq_flusher {
         struct list_head        list;           /* WQ: list of flushers */
         int                     flush_color;    /* WQ: flush color waiting for */
         struct completion       done;           /* flush completion */
 };
 
 struct wq_device;
 
 /*
  * Unlike in a per-cpu workqueue where max_active limits its concurrency level
  * on each CPU, in an unbound workqueue, max_active applies to the whole system.
  * As sharing a single nr_active across multiple sockets can be very expensive,
  * the counting and enforcement is per NUMA node.
  *
  * The following struct is used to enforce per-node max_active. When a pwq wants
  * to start executing a work item, it should increment ->nr using
  * tryinc_node_nr_active(). If acquisition fails due to ->nr already being over
  * ->max, the pwq is queued on ->pending_pwqs. As in-flight work items finish
  * and decrement ->nr, node_activate_pending_pwq() activates the pending pwqs in
  * round-robin order.
  */
 struct wq_node_nr_active {
         int                     max;            /* per-node max_active */
         atomic_t                nr;             /* per-node nr_active */
         raw_spinlock_t          lock;           /* nests inside pool locks */
         struct list_head        pending_pwqs;   /* LN: pwqs with inactive works */
 };
 
 /*
  * The externally visible workqueue.  It relays the issued work items to
  * the appropriate worker_pool through its pool_workqueues.
  */
 struct workqueue_struct {
         struct list_head        pwqs;           /* WR: all pwqs of this wq */
         struct list_head        list;           /* PR: list of all workqueues */
 
         struct mutex            mutex;          /* protects this wq */
         int                     work_color;     /* WQ: current work color */
         int                     flush_color;    /* WQ: current flush color */
         atomic_t                nr_pwqs_to_flush; /* flush in progress */
         struct wq_flusher       *first_flusher; /* WQ: first flusher */
         struct list_head        flusher_queue;  /* WQ: flush waiters */
         struct list_head        flusher_overflow; /* WQ: flush overflow list */
 
         struct list_head        maydays;        /* MD: pwqs requesting rescue */
         struct worker           *rescuer;       /* MD: rescue worker */
 
         int                     nr_drainers;    /* WQ: drain in progress */
 
         /* See alloc_workqueue() function comment for info on min/max_active */
         int                     max_active;     /* WO: max active works */
         int                     min_active;     /* WO: min active works */
         int                     saved_max_active; /* WQ: saved max_active */
         int                     saved_min_active; /* WQ: saved min_active */
 
         struct workqueue_attrs  *unbound_attrs; /* PW: only for unbound wqs */
         struct pool_workqueue __rcu *dfl_pwq;   /* PW: only for unbound wqs */
 
 #ifdef CONFIG_SYSFS
         struct wq_device        *wq_dev;        /* I: for sysfs interface */
 #endif
 #ifdef CONFIG_LOCKDEP
         char                    *lock_name;
         struct lock_class_key   key;
         struct lockdep_map      lockdep_map;
 #endif
         char                    name[WQ_NAME_LEN]; /* I: workqueue name */
 
         /*
          * Destruction of workqueue_struct is RCU protected to allow walking
          * the workqueues list without grabbing wq_pool_mutex.
          * This is used to dump all workqueues from sysrq.
          */
         struct rcu_head         rcu;
 
         /* hot fields used during command issue, aligned to cacheline */
         unsigned int            flags ____cacheline_aligned; /* WQ: WQ_* flags */
         struct pool_workqueue __percpu __rcu **cpu_pwq; /* I: per-cpu pwqs */
         struct wq_node_nr_active *node_nr_active[]; /* I: per-node nr_active */
 };
 
 /*
  * Each pod type describes how CPUs should be grouped for unbound workqueues.
  * See the comment above workqueue_attrs->affn_scope.
  */
 struct wq_pod_type {
         int                     nr_pods;        /* number of pods */
         cpumask_var_t           *pod_cpus;      /* pod -> cpus */
         int                     *pod_node;      /* pod -> node */
         int                     *cpu_pod;       /* cpu -> pod */
 };
 
 struct work_offq_data {
         u32                     pool_id;
         u32                     disable;
         u32                     flags;
 };
 
 static const char *wq_affn_names[WQ_AFFN_NR_TYPES] = {
         [WQ_AFFN_DFL]           = "default",
         [WQ_AFFN_CPU]           = "cpu",
         [WQ_AFFN_SMT]           = "smt",
         [WQ_AFFN_CACHE]         = "cache",
         [WQ_AFFN_NUMA]          = "numa",
         [WQ_AFFN_SYSTEM]        = "system",
 };
 
 /*
  * Per-cpu work items which run for longer than the following threshold are
  * automatically considered CPU intensive and excluded from concurrency
  * management to prevent them from noticeably delaying other per-cpu work items.
  * ULONG_MAX indicates that the user hasn't overridden it with a boot parameter.
  * The actual value is initialized in wq_cpu_intensive_thresh_init().
  */
 static unsigned long wq_cpu_intensive_thresh_us = ULONG_MAX;
 module_param_named(cpu_intensive_thresh_us, wq_cpu_intensive_thresh_us, ulong, 0644);
 #ifdef CONFIG_WQ_CPU_INTENSIVE_REPORT
 static unsigned int wq_cpu_intensive_warning_thresh = 4;
 module_param_named(cpu_intensive_warning_thresh, wq_cpu_intensive_warning_thresh, uint, 0644);
 #endif
 
 /* see the comment above the definition of WQ_POWER_EFFICIENT */
 static bool wq_power_efficient = IS_ENABLED(CONFIG_WQ_POWER_EFFICIENT_DEFAULT);
 module_param_named(power_efficient, wq_power_efficient, bool, 0444);
 
 static bool wq_online;                  /* can kworkers be created yet? */
 static bool wq_topo_initialized __read_mostly = false;
 
 static struct kmem_cache *pwq_cache;
 
 static struct wq_pod_type wq_pod_types[WQ_AFFN_NR_TYPES];
 static enum wq_affn_scope wq_affn_dfl = WQ_AFFN_CACHE;
 
 /* buf for wq_update_unbound_pod_attrs(), protected by CPU hotplug exclusion */
 static struct workqueue_attrs *unbound_wq_update_pwq_attrs_buf;
 
 static DEFINE_MUTEX(wq_pool_mutex);     /* protects pools and workqueues list */
 static DEFINE_MUTEX(wq_pool_attach_mutex); /* protects worker attach/detach */
 static DEFINE_RAW_SPINLOCK(wq_mayday_lock);     /* protects wq->maydays list */
 /* wait for manager to go away */
 static struct rcuwait manager_wait = __RCUWAIT_INITIALIZER(manager_wait);
 
 static LIST_HEAD(workqueues);           /* PR: list of all workqueues */
 static bool workqueue_freezing;         /* PL: have wqs started freezing? */
 
 /* PL: mirror the cpu_online_mask excluding the CPU in the midst of hotplugging */
 static cpumask_var_t wq_online_cpumask;
 
 /* PL&A: allowable cpus for unbound wqs and work items */
 static cpumask_var_t wq_unbound_cpumask;
 
 /* PL: user requested unbound cpumask via sysfs */
 static cpumask_var_t wq_requested_unbound_cpumask;
 
 /* PL: isolated cpumask to be excluded from unbound cpumask */
 static cpumask_var_t wq_isolated_cpumask;
 
 /* for further constrain wq_unbound_cpumask by cmdline parameter*/
 static struct cpumask wq_cmdline_cpumask __initdata;
 
 /* CPU where unbound work was last round robin scheduled from this CPU */
 static DEFINE_PER_CPU(int, wq_rr_cpu_last);
 
 /*
  * Local execution of unbound work items is no longer guaranteed.  The
  * following always forces round-robin CPU selection on unbound work items
  * to uncover usages which depend on it.
  */
 #ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
 static bool wq_debug_force_rr_cpu = true;
 #else
 static bool wq_debug_force_rr_cpu = false;
 #endif
 module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);
 
 /* to raise softirq for the BH worker pools on other CPUs */
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct irq_work [NR_STD_WORKER_POOLS],
                                      bh_pool_irq_works);
 
 /* the BH worker pools */
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
                                      bh_worker_pools);
 
 /* the per-cpu worker pools */
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
                                      cpu_worker_pools);
 
 static DEFINE_IDR(worker_pool_idr);     /* PR: idr of all pools */
 
 /* PL: hash of all unbound pools keyed by pool->attrs */
 static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
 
 /* I: attributes used when instantiating standard unbound pools on demand */
 static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
 
 /* I: attributes used when instantiating ordered pools on demand */
 static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];
 
 /*
  * I: kthread_worker to release pwq's. pwq release needs to be bounced to a
  * process context while holding a pool lock. Bounce to a dedicated kthread
  * worker to avoid A-A deadlocks.
  */
 static struct kthread_worker *pwq_release_worker __ro_after_init;
 
 struct workqueue_struct *system_wq __ro_after_init;
 EXPORT_SYMBOL(system_wq);
 struct workqueue_struct *system_highpri_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_highpri_wq);
 struct workqueue_struct *system_long_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_long_wq);
 struct workqueue_struct *system_unbound_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_unbound_wq);
 struct workqueue_struct *system_freezable_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_freezable_wq);
 struct workqueue_struct *system_power_efficient_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_power_efficient_wq);
 struct workqueue_struct *system_freezable_power_efficient_wq __ro_after_init;
 EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
 struct workqueue_struct *system_bh_wq;
 EXPORT_SYMBOL_GPL(system_bh_wq);
 struct workqueue_struct *system_bh_highpri_wq;
 EXPORT_SYMBOL_GPL(system_bh_highpri_wq);
 
 static int worker_thread(void *__worker);
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
 static void show_pwq(struct pool_workqueue *pwq);
 static void show_one_worker_pool(struct worker_pool *pool);
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/workqueue.h>
 
 #define assert_rcu_or_pool_mutex()                                      \
         RCU_LOCKDEP_WARN(!rcu_read_lock_any_held() &&                   \
                          !lockdep_is_held(&wq_pool_mutex),              \
                          "RCU or wq_pool_mutex should be held")
 
 #define assert_rcu_or_wq_mutex_or_pool_mutex(wq)                        \
         RCU_LOCKDEP_WARN(!rcu_read_lock_any_held() &&                   \
                          !lockdep_is_held(&wq->mutex) &&                \
                          !lockdep_is_held(&wq_pool_mutex),              \
                          "RCU, wq->mutex or wq_pool_mutex should be held")
 
 #define for_each_bh_worker_pool(pool, cpu)                              \
         for ((pool) = &per_cpu(bh_worker_pools, cpu)[0];                \
              (pool) < &per_cpu(bh_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
              (pool)++)
 
 #define for_each_cpu_worker_pool(pool, cpu)                             \
         for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];               \
              (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
              (pool)++)
 
 /**
  * for_each_pool - iterate through all worker_pools in the system
  * @pool: iteration cursor
  * @pi: integer used for iteration
  *
  * This must be called either with wq_pool_mutex held or RCU read
  * locked.  If the pool needs to be used beyond the locking in effect, the
  * caller is responsible for guaranteeing that the pool stays online.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pool(pool, pi)                                         \
         idr_for_each_entry(&worker_pool_idr, pool, pi)                  \
                 if (({ assert_rcu_or_pool_mutex(); false; })) { }       \
                 else
 
 /**
  * for_each_pool_worker - iterate through all workers of a worker_pool
  * @worker: iteration cursor
  * @pool: worker_pool to iterate workers of
  *
  * This must be called with wq_pool_attach_mutex.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pool_worker(worker, pool)                              \
         list_for_each_entry((worker), &(pool)->workers, node)           \
                 if (({ lockdep_assert_held(&wq_pool_attach_mutex); false; })) { } \
                 else
 
 /**
  * for_each_pwq - iterate through all pool_workqueues of the specified workqueue
  * @pwq: iteration cursor
  * @wq: the target workqueue
  *
  * This must be called either with wq->mutex held or RCU read locked.
  * If the pwq needs to be used beyond the locking in effect, the caller is
  * responsible for guaranteeing that the pwq stays online.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pwq(pwq, wq)                                           \
         list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,          \
                                  lockdep_is_held(&(wq->mutex)))
 
 #ifdef CONFIG_DEBUG_OBJECTS_WORK
 
 static const struct debug_obj_descr work_debug_descr;
 
 static void *work_debug_hint(void *addr)
 {
         return ((struct work_struct *) addr)->func;
 }
 
 static bool work_is_static_object(void *addr)
 {
         struct work_struct *work = addr;
 
         return test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work));
 }
 
 /*
  * fixup_init is called when:
  * - an active object is initialized
  */
 static bool work_fixup_init(void *addr, enum debug_obj_state state)
 {
         struct work_struct *work = addr;
 
         switch (state) {
         case ODEBUG_STATE_ACTIVE:
                 cancel_work_sync(work);
                 debug_object_init(work, &work_debug_descr);
                 return true;
         default:
                 return false;
         }
 }
 
 /*
  * fixup_free is called when:
  * - an active object is freed
  */
 static bool work_fixup_free(void *addr, enum debug_obj_state state)
 {
         struct work_struct *work = addr;
 
         switch (state) {
         case ODEBUG_STATE_ACTIVE:
                 cancel_work_sync(work);
                 debug_object_free(work, &work_debug_descr);
                 return true;
         default:
                 return false;
         }
 }
 
 static const struct debug_obj_descr work_debug_descr = {
         .name           = "work_struct",
         .debug_hint     = work_debug_hint,
         .is_static_object = work_is_static_object,
         .fixup_init     = work_fixup_init,
         .fixup_free     = work_fixup_free,
 };
 
 static inline void debug_work_activate(struct work_struct *work)
 {
         debug_object_activate(work, &work_debug_descr);
 }
 
 static inline void debug_work_deactivate(struct work_struct *work)
 {
         debug_object_deactivate(work, &work_debug_descr);
 }
 
 void __init_work(struct work_struct *work, int onstack)
 {
         if (onstack)
                 debug_object_init_on_stack(work, &work_debug_descr);
         else
                 debug_object_init(work, &work_debug_descr);
 }
 EXPORT_SYMBOL_GPL(__init_work);
 
 void destroy_work_on_stack(struct work_struct *work)
 {
         debug_object_free(work, &work_debug_descr);
 }
 EXPORT_SYMBOL_GPL(destroy_work_on_stack);
 
 void destroy_delayed_work_on_stack(struct delayed_work *work)
 {
         destroy_timer_on_stack(&work->timer);
         debug_object_free(&work->work, &work_debug_descr);
 }
 EXPORT_SYMBOL_GPL(destroy_delayed_work_on_stack);
 
 #else
 static inline void debug_work_activate(struct work_struct *work) { }
 static inline void debug_work_deactivate(struct work_struct *work) { }
 #endif
 
 /**
  * worker_pool_assign_id - allocate ID and assign it to @pool
  * @pool: the pool pointer of interest
  *
  * Returns 0 if ID in [0, WORK_OFFQ_POOL_NONE) is allocated and assigned
  * successfully, -errno on failure.
  */
 static int worker_pool_assign_id(struct worker_pool *pool)
 {
         int ret;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         ret = idr_alloc(&worker_pool_idr, pool, 0, WORK_OFFQ_POOL_NONE,
                         GFP_KERNEL);
         if (ret >= 0) {
                 pool->id = ret;
                 return 0;
         }
         return ret;
 }
 
 static struct pool_workqueue __rcu **
 unbound_pwq_slot(struct workqueue_struct *wq, int cpu)
 {
        if (cpu >= 0)
                return per_cpu_ptr(wq->cpu_pwq, cpu);
        else
                return &wq->dfl_pwq;
 }
 
 /* @cpu < 0 for dfl_pwq */
 static struct pool_workqueue *unbound_pwq(struct workqueue_struct *wq, int cpu)
 {
         return rcu_dereference_check(*unbound_pwq_slot(wq, cpu),
                                      lockdep_is_held(&wq_pool_mutex) ||
                                      lockdep_is_held(&wq->mutex));
 }
 
 /**
  * unbound_effective_cpumask - effective cpumask of an unbound workqueue
  * @wq: workqueue of interest
  *
  * @wq->unbound_attrs->cpumask contains the cpumask requested by the user which
  * is masked with wq_unbound_cpumask to determine the effective cpumask. The
  * default pwq is always mapped to the pool with the current effective cpumask.
  */
 static struct cpumask *unbound_effective_cpumask(struct workqueue_struct *wq)
 {
         return unbound_pwq(wq, -1)->pool->attrs->__pod_cpumask;
 }
 
 static unsigned int work_color_to_flags(int color)
 {
         return color << WORK_STRUCT_COLOR_SHIFT;
 }
 
 static int get_work_color(unsigned long work_data)
 {
         return (work_data >> WORK_STRUCT_COLOR_SHIFT) &
                 ((1 << WORK_STRUCT_COLOR_BITS) - 1);
 }
 
 static int work_next_color(int color)
 {
         return (color + 1) % WORK_NR_COLORS;
 }
 
 static unsigned long pool_offq_flags(struct worker_pool *pool)
 {
         return (pool->flags & POOL_BH) ? WORK_OFFQ_BH : 0;
 }
 
 /*
  * While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
  * contain the pointer to the queued pwq.  Once execution starts, the flag
  * is cleared and the high bits contain OFFQ flags and pool ID.
  *
  * set_work_pwq(), set_work_pool_and_clear_pending() and mark_work_canceling()
  * can be used to set the pwq, pool or clear work->data. These functions should
  * only be called while the work is owned - ie. while the PENDING bit is set.
  *
  * get_work_pool() and get_work_pwq() can be used to obtain the pool or pwq
  * corresponding to a work.  Pool is available once the work has been
  * queued anywhere after initialization until it is sync canceled.  pwq is
  * available only while the work item is queued.
  */
 static inline void set_work_data(struct work_struct *work, unsigned long data)
 {
         WARN_ON_ONCE(!work_pending(work));
         atomic_long_set(&work->data, data | work_static(work));
 }
 
 static void set_work_pwq(struct work_struct *work, struct pool_workqueue *pwq,
                          unsigned long flags)
 {
         set_work_data(work, (unsigned long)pwq | WORK_STRUCT_PENDING |
                       WORK_STRUCT_PWQ | flags);
 }
 
 static void set_work_pool_and_keep_pending(struct work_struct *work,
                                            int pool_id, unsigned long flags)
 {
         set_work_data(work, ((unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT) |
                       WORK_STRUCT_PENDING | flags);
 }
 
 static void set_work_pool_and_clear_pending(struct work_struct *work,
                                             int pool_id, unsigned long flags)
 {
         /*
          * The following wmb is paired with the implied mb in
          * test_and_set_bit(PENDING) and ensures all updates to @work made
          * here are visible to and precede any updates by the next PENDING
          * owner.
          */
         smp_wmb();
         set_work_data(work, ((unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT) |
                       flags);
         /*
          * The following mb guarantees that previous clear of a PENDING bit
          * will not be reordered with any speculative LOADS or STORES from
          * work->current_func, which is executed afterwards.  This possible
          * reordering can lead to a missed execution on attempt to queue
          * the same @work.  E.g. consider this case:
          *
          *   CPU#0                         CPU#1
          *   ----------------------------  --------------------------------
          *
          * 1  STORE event_indicated
          * 2  queue_work_on() {
          * 3    test_and_set_bit(PENDING)
          * 4 }                             set_..._and_clear_pending() {
          * 5                                 set_work_data() # clear bit
          * 6                                 smp_mb()
          * 7                               work->current_func() {
          * 8                                  LOAD event_indicated
          *                                 }
          *
          * Without an explicit full barrier speculative LOAD on line 8 can
          * be executed before CPU#0 does STORE on line 1.  If that happens,
          * CPU#0 observes the PENDING bit is still set and new execution of
          * a @work is not queued in a hope, that CPU#1 will eventually
          * finish the queued @work.  Meanwhile CPU#1 does not see
          * event_indicated is set, because speculative LOAD was executed
          * before actual STORE.
          */
         smp_mb();
 }
 
 static inline struct pool_workqueue *work_struct_pwq(unsigned long data)
 {
         return (struct pool_workqueue *)(data & WORK_STRUCT_PWQ_MASK);
 }
 
 static struct pool_workqueue *get_work_pwq(struct work_struct *work)
 {
         unsigned long data = atomic_long_read(&work->data);
 
         if (data & WORK_STRUCT_PWQ)
                 return work_struct_pwq(data);
         else
                 return NULL;
 }
 
 /**
  * get_work_pool - return the worker_pool a given work was associated with
  * @work: the work item of interest
  *
  * Pools are created and destroyed under wq_pool_mutex, and allows read
  * access under RCU read lock.  As such, this function should be
  * called under wq_pool_mutex or inside of a rcu_read_lock() region.
  *
  * All fields of the returned pool are accessible as long as the above
  * mentioned locking is in effect.  If the returned pool needs to be used
  * beyond the critical section, the caller is responsible for ensuring the
  * returned pool is and stays online.
  *
  * Return: The worker_pool @work was last associated with.  %NULL if none.
  */
 static struct worker_pool *get_work_pool(struct work_struct *work)
 {
         unsigned long data = atomic_long_read(&work->data);
         int pool_id;
 
         assert_rcu_or_pool_mutex();
 
         if (data & WORK_STRUCT_PWQ)
                 return work_struct_pwq(data)->pool;
 
         pool_id = data >> WORK_OFFQ_POOL_SHIFT;
         if (pool_id == WORK_OFFQ_POOL_NONE)
                 return NULL;
 
         return idr_find(&worker_pool_idr, pool_id);
 }
 
 static unsigned long shift_and_mask(unsigned long v, u32 shift, u32 bits)
 {
         return (v >> shift) & ((1 << bits) - 1);
 }
 
 static void work_offqd_unpack(struct work_offq_data *offqd, unsigned long data)
 {
         WARN_ON_ONCE(data & WORK_STRUCT_PWQ);
 
         offqd->pool_id = shift_and_mask(data, WORK_OFFQ_POOL_SHIFT,
                                         WORK_OFFQ_POOL_BITS);
         offqd->disable = shift_and_mask(data, WORK_OFFQ_DISABLE_SHIFT,
                                         WORK_OFFQ_DISABLE_BITS);
         offqd->flags = data & WORK_OFFQ_FLAG_MASK;
 }
 
 static unsigned long work_offqd_pack_flags(struct work_offq_data *offqd)
 {
         return ((unsigned long)offqd->disable << WORK_OFFQ_DISABLE_SHIFT) |
                 ((unsigned long)offqd->flags);
 }
 
 /*
  * Policy functions.  These define the policies on how the global worker
  * pools are managed.  Unless noted otherwise, these functions assume that
  * they're being called with pool->lock held.
  */
 
 /*
  * Need to wake up a worker?  Called from anything but currently
  * running workers.
  *
  * Note that, because unbound workers never contribute to nr_running, this
  * function will always return %true for unbound pools as long as the
  * worklist isn't empty.
  */
 static bool need_more_worker(struct worker_pool *pool)
 {
         return !list_empty(&pool->worklist) && !pool->nr_running;
 }
 
 /* Can I start working?  Called from busy but !running workers. */
 static bool may_start_working(struct worker_pool *pool)
 {
         return pool->nr_idle;
 }
 
 /* Do I need to keep working?  Called from currently running workers. */
 static bool keep_working(struct worker_pool *pool)
 {
         return !list_empty(&pool->worklist) && (pool->nr_running <= 1);
 }
 
 /* Do we need a new worker?  Called from manager. */
 static bool need_to_create_worker(struct worker_pool *pool)
 {
         return need_more_worker(pool) && !may_start_working(pool);
 }
 
 /* Do we have too many workers and should some go away? */
 static bool too_many_workers(struct worker_pool *pool)
 {
         bool managing = pool->flags & POOL_MANAGER_ACTIVE;
         int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
         int nr_busy = pool->nr_workers - nr_idle;
 
         return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
 }
 
 /**
  * worker_set_flags - set worker flags and adjust nr_running accordingly
  * @worker: self
  * @flags: flags to set
  *
  * Set @flags in @worker->flags and adjust nr_running accordingly.
  */
 static inline void worker_set_flags(struct worker *worker, unsigned int flags)
 {
         struct worker_pool *pool = worker->pool;
 
         lockdep_assert_held(&pool->lock);
 
         /* If transitioning into NOT_RUNNING, adjust nr_running. */
         if ((flags & WORKER_NOT_RUNNING) &&
             !(worker->flags & WORKER_NOT_RUNNING)) {
                 pool->nr_running--;
         }
 
         worker->flags |= flags;
 }
 
 /**
  * worker_clr_flags - clear worker flags and adjust nr_running accordingly
  * @worker: self
  * @flags: flags to clear
  *
  * Clear @flags in @worker->flags and adjust nr_running accordingly.
  */
 static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
 {
         struct worker_pool *pool = worker->pool;
         unsigned int oflags = worker->flags;
 
         lockdep_assert_held(&pool->lock);
 
         worker->flags &= ~flags;
 
         /*
          * If transitioning out of NOT_RUNNING, increment nr_running.  Note
          * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
          * of multiple flags, not a single flag.
          */
         if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
                 if (!(worker->flags & WORKER_NOT_RUNNING))
                         pool->nr_running++;
 }
 
 /* Return the first idle worker.  Called with pool->lock held. */
 static struct worker *first_idle_worker(struct worker_pool *pool)
 {
         if (unlikely(list_empty(&pool->idle_list)))
                 return NULL;
 
         return list_first_entry(&pool->idle_list, struct worker, entry);
 }
 
 /**
  * worker_enter_idle - enter idle state
  * @worker: worker which is entering idle state
  *
  * @worker is entering idle state.  Update stats and idle timer if
  * necessary.
  *
  * LOCKING:
  * raw_spin_lock_irq(pool->lock).
  */
 static void worker_enter_idle(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
 
         if (WARN_ON_ONCE(worker->flags & WORKER_IDLE) ||
             WARN_ON_ONCE(!list_empty(&worker->entry) &&
                          (worker->hentry.next || worker->hentry.pprev)))
                 return;
 
         /* can't use worker_set_flags(), also called from create_worker() */
         worker->flags |= WORKER_IDLE;
         pool->nr_idle++;
         worker->last_active = jiffies;
 
         /* idle_list is LIFO */
         list_add(&worker->entry, &pool->idle_list);
 
         if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
                 mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);
 
         /* Sanity check nr_running. */
         WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
 }
 
 /**
  * worker_leave_idle - leave idle state
  * @worker: worker which is leaving idle state
  *
  * @worker is leaving idle state.  Update stats.
  *
  * LOCKING:
  * raw_spin_lock_irq(pool->lock).
  */
 static void worker_leave_idle(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
 
         if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
                 return;
         worker_clr_flags(worker, WORKER_IDLE);
         pool->nr_idle--;
         list_del_init(&worker->entry);
 }
 
 /**
  * find_worker_executing_work - find worker which is executing a work
  * @pool: pool of interest
  * @work: work to find worker for
  *
  * Find a worker which is executing @work on @pool by searching
  * @pool->busy_hash which is keyed by the address of @work.  For a worker
  * to match, its current execution should match the address of @work and
  * its work function.  This is to avoid unwanted dependency between
  * unrelated work executions through a work item being recycled while still
  * being executed.
  *
  * This is a bit tricky.  A work item may be freed once its execution
  * starts and nothing prevents the freed area from being recycled for
  * another work item.  If the same work item address ends up being reused
  * before the original execution finishes, workqueue will identify the
  * recycled work item as currently executing and make it wait until the
  * current execution finishes, introducing an unwanted dependency.
  *
  * This function checks the work item address and work function to avoid
  * false positives.  Note that this isn't complete as one may construct a
  * work function which can introduce dependency onto itself through a
  * recycled work item.  Well, if somebody wants to shoot oneself in the
  * foot that badly, there's only so much we can do, and if such deadlock
  * actually occurs, it should be easy to locate the culprit work function.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  *
  * Return:
  * Pointer to worker which is executing @work if found, %NULL
  * otherwise.
  */
 static struct worker *find_worker_executing_work(struct worker_pool *pool,
                                                  struct work_struct *work)
 {
         struct worker *worker;
 
         hash_for_each_possible(pool->busy_hash, worker, hentry,
                                (unsigned long)work)
                 if (worker->current_work == work &&
                     worker->current_func == work->func)
                         return worker;
 
         return NULL;
 }
 
 /**
  * move_linked_works - move linked works to a list
  * @work: start of series of works to be scheduled
  * @head: target list to append @work to
  * @nextp: out parameter for nested worklist walking
  *
  * Schedule linked works starting from @work to @head. Work series to be
  * scheduled starts at @work and includes any consecutive work with
  * WORK_STRUCT_LINKED set in its predecessor. See assign_work() for details on
  * @nextp.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void move_linked_works(struct work_struct *work, struct list_head *head,
                               struct work_struct **nextp)
 {
         struct work_struct *n;
 
         /*
          * Linked worklist will always end before the end of the list,
          * use NULL for list head.
          */
         list_for_each_entry_safe_from(work, n, NULL, entry) {
                 list_move_tail(&work->entry, head);
                 if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
                         break;
         }
 
         /*
          * If we're already inside safe list traversal and have moved
          * multiple works to the scheduled queue, the next position
          * needs to be updated.
          */
         if (nextp)
                 *nextp = n;
 }
 
 /**
  * assign_work - assign a work item and its linked work items to a worker
  * @work: work to assign
  * @worker: worker to assign to
  * @nextp: out parameter for nested worklist walking
  *
  * Assign @work and its linked work items to @worker. If @work is already being
  * executed by another worker in the same pool, it'll be punted there.
  *
  * If @nextp is not NULL, it's updated to point to the next work of the last
  * scheduled work. This allows assign_work() to be nested inside
  * list_for_each_entry_safe().
  *
  * Returns %true if @work was successfully assigned to @worker. %false if @work
  * was punted to another worker already executing it.
  */
 static bool assign_work(struct work_struct *work, struct worker *worker,
                         struct work_struct **nextp)
 {
         struct worker_pool *pool = worker->pool;
         struct worker *collision;
 
         lockdep_assert_held(&pool->lock);
 
         /*
          * A single work shouldn't be executed concurrently by multiple workers.
          * __queue_work() ensures that @work doesn't jump to a different pool
          * while still running in the previous pool. Here, we should ensure that
          * @work is not executed concurrently by multiple workers from the same
          * pool. Check whether anyone is already processing the work. If so,
          * defer the work to the currently executing one.
          */
         collision = find_worker_executing_work(pool, work);
         if (unlikely(collision)) {
                 move_linked_works(work, &collision->scheduled, nextp);
                 return false;
         }
 
         move_linked_works(work, &worker->scheduled, nextp);
         return true;
 }
 
 static struct irq_work *bh_pool_irq_work(struct worker_pool *pool)
 {
         int high = pool->attrs->nice == HIGHPRI_NICE_LEVEL ? 1 : 0;
 
         return &per_cpu(bh_pool_irq_works, pool->cpu)[high];
 }
 
 static void kick_bh_pool(struct worker_pool *pool)
 {
 #ifdef CONFIG_SMP
         /* see drain_dead_softirq_workfn() for BH_DRAINING */
         if (unlikely(pool->cpu != smp_processor_id() &&
                      !(pool->flags & POOL_BH_DRAINING))) {
                 irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
                 return;
         }
 #endif
         if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
                 raise_softirq_irqoff(HI_SOFTIRQ);
         else
                 raise_softirq_irqoff(TASKLET_SOFTIRQ);
 }
 
 /**
  * kick_pool - wake up an idle worker if necessary
  * @pool: pool to kick
  *
  * @pool may have pending work items. Wake up worker if necessary. Returns
  * whether a worker was woken up.
  */
 static bool kick_pool(struct worker_pool *pool)
 {
         struct worker *worker = first_idle_worker(pool);
         struct task_struct *p;
 
         lockdep_assert_held(&pool->lock);
 
         if (!need_more_worker(pool) || !worker)
                 return false;
 
         if (pool->flags & POOL_BH) {
                 kick_bh_pool(pool);
                 return true;
         }
 
         p = worker->task;
 
 #ifdef CONFIG_SMP
         /*
          * Idle @worker is about to execute @work and waking up provides an
          * opportunity to migrate @worker at a lower cost by setting the task's
          * wake_cpu field. Let's see if we want to move @worker to improve
          * execution locality.
          *
          * We're waking the worker that went idle the latest and there's some
          * chance that @worker is marked idle but hasn't gone off CPU yet. If
          * so, setting the wake_cpu won't do anything. As this is a best-effort
          * optimization and the race window is narrow, let's leave as-is for
          * now. If this becomes pronounced, we can skip over workers which are
          * still on cpu when picking an idle worker.
          *
          * If @pool has non-strict affinity, @worker might have ended up outside
          * its affinity scope. Repatriate.
          */
         if (!pool->attrs->affn_strict &&
             !cpumask_test_cpu(p->wake_cpu, pool->attrs->__pod_cpumask)) {
                 struct work_struct *work = list_first_entry(&pool->worklist,
                                                 struct work_struct, entry);
                 int wake_cpu = cpumask_any_and_distribute(pool->attrs->__pod_cpumask,
                                                           cpu_online_mask);
                 if (wake_cpu < nr_cpu_ids) {
                         p->wake_cpu = wake_cpu;
                         get_work_pwq(work)->stats[PWQ_STAT_REPATRIATED]++;
                 }
         }
 #endif
         wake_up_process(p);
         return true;
 }
 
 #ifdef CONFIG_WQ_CPU_INTENSIVE_REPORT
 
 /*
  * Concurrency-managed per-cpu work items that hog CPU for longer than
  * wq_cpu_intensive_thresh_us trigger the automatic CPU_INTENSIVE mechanism,
  * which prevents them from stalling other concurrency-managed work items. If a
  * work function keeps triggering this mechanism, it's likely that the work item
  * should be using an unbound workqueue instead.
  *
  * wq_cpu_intensive_report() tracks work functions which trigger such conditions
  * and report them so that they can be examined and converted to use unbound
  * workqueues as appropriate. To avoid flooding the console, each violating work
  * function is tracked and reported with exponential backoff.
  */
 #define WCI_MAX_ENTS 128
 
 struct wci_ent {
         work_func_t             func;
         atomic64_t              cnt;
         struct hlist_node       hash_node;
 };
 
 static struct wci_ent wci_ents[WCI_MAX_ENTS];
 static int wci_nr_ents;
 static DEFINE_RAW_SPINLOCK(wci_lock);
 static DEFINE_HASHTABLE(wci_hash, ilog2(WCI_MAX_ENTS));
 
 static struct wci_ent *wci_find_ent(work_func_t func)
 {
         struct wci_ent *ent;
 
         hash_for_each_possible_rcu(wci_hash, ent, hash_node,
                                    (unsigned long)func) {
                 if (ent->func == func)
                         return ent;
         }
         return NULL;
 }
 
 static void wq_cpu_intensive_report(work_func_t func)
 {
         struct wci_ent *ent;
 
 restart:
         ent = wci_find_ent(func);
         if (ent) {
                 u64 cnt;
 
                 /*
                  * Start reporting from the warning_thresh and back off
                  * exponentially.
                  */
                 cnt = atomic64_inc_return_relaxed(&ent->cnt);
                 if (wq_cpu_intensive_warning_thresh &&
                     cnt >= wq_cpu_intensive_warning_thresh &&
                     is_power_of_2(cnt + 1 - wq_cpu_intensive_warning_thresh))
                         printk_deferred(KERN_WARNING "workqueue: %ps hogged CPU for >%luus %llu times, consider switching to WQ_UNBOUND\n",
                                         ent->func, wq_cpu_intensive_thresh_us,
                                         atomic64_read(&ent->cnt));
                 return;
         }
 
         /*
          * @func is a new violation. Allocate a new entry for it. If wcn_ents[]
          * is exhausted, something went really wrong and we probably made enough
          * noise already.
          */
         if (wci_nr_ents >= WCI_MAX_ENTS)
                 return;
 
         raw_spin_lock(&wci_lock);
 
         if (wci_nr_ents >= WCI_MAX_ENTS) {
                 raw_spin_unlock(&wci_lock);
                 return;
         }
 
         if (wci_find_ent(func)) {
                 raw_spin_unlock(&wci_lock);
                 goto restart;
         }
 
         ent = &wci_ents[wci_nr_ents++];
         ent->func = func;
         atomic64_set(&ent->cnt, 0);
         hash_add_rcu(wci_hash, &ent->hash_node, (unsigned long)func);
 
         raw_spin_unlock(&wci_lock);
 
         goto restart;
 }
 
 #else   /* CONFIG_WQ_CPU_INTENSIVE_REPORT */
 static void wq_cpu_intensive_report(work_func_t func) {}
 #endif  /* CONFIG_WQ_CPU_INTENSIVE_REPORT */
 
 /**
  * wq_worker_running - a worker is running again
  * @task: task waking up
  *
  * This function is called when a worker returns from schedule()
  */
 void wq_worker_running(struct task_struct *task)
 {
         struct worker *worker = kthread_data(task);
 
         if (!READ_ONCE(worker->sleeping))
                 return;
 
         /*
          * If preempted by unbind_workers() between the WORKER_NOT_RUNNING check
          * and the nr_running increment below, we may ruin the nr_running reset
          * and leave with an unexpected pool->nr_running == 1 on the newly unbound
          * pool. Protect against such race.
          */
         preempt_disable();
         if (!(worker->flags & WORKER_NOT_RUNNING))
                 worker->pool->nr_running++;
         preempt_enable();
 
         /*
          * CPU intensive auto-detection cares about how long a work item hogged
          * CPU without sleeping. Reset the starting timestamp on wakeup.
          */
         worker->current_at = worker->task->se.sum_exec_runtime;
 
         WRITE_ONCE(worker->sleeping, 0);
 }
 
 /**
  * wq_worker_sleeping - a worker is going to sleep
  * @task: task going to sleep
  *
  * This function is called from schedule() when a busy worker is
  * going to sleep.
  */
 void wq_worker_sleeping(struct task_struct *task)
 {
         struct worker *worker = kthread_data(task);
         struct worker_pool *pool;
 
         /*
          * Rescuers, which may not have all the fields set up like normal
          * workers, also reach here, let's not access anything before
          * checking NOT_RUNNING.
          */
         if (worker->flags & WORKER_NOT_RUNNING)
                 return;
 
         pool = worker->pool;
 
         /* Return if preempted before wq_worker_running() was reached */
         if (READ_ONCE(worker->sleeping))
                 return;
 
         WRITE_ONCE(worker->sleeping, 1);
         raw_spin_lock_irq(&pool->lock);
 
         /*
          * Recheck in case unbind_workers() preempted us. We don't
          * want to decrement nr_running after the worker is unbound
          * and nr_running has been reset.
          */
         if (worker->flags & WORKER_NOT_RUNNING) {
                 raw_spin_unlock_irq(&pool->lock);
                 return;
         }
 
         pool->nr_running--;
         if (kick_pool(pool))
                 worker->current_pwq->stats[PWQ_STAT_CM_WAKEUP]++;
 
         raw_spin_unlock_irq(&pool->lock);
 }
 
 /**
  * wq_worker_tick - a scheduler tick occurred while a kworker is running
  * @task: task currently running
  *
  * Called from sched_tick(). We're in the IRQ context and the current
  * worker's fields which follow the 'K' locking rule can be accessed safely.
  */
 void wq_worker_tick(struct task_struct *task)
 {
         struct worker *worker = kthread_data(task);
         struct pool_workqueue *pwq = worker->current_pwq;
         struct worker_pool *pool = worker->pool;
 
         if (!pwq)
                 return;
 
         pwq->stats[PWQ_STAT_CPU_TIME] += TICK_USEC;
 
         if (!wq_cpu_intensive_thresh_us)
                 return;
 
         /*
          * If the current worker is concurrency managed and hogged the CPU for
          * longer than wq_cpu_intensive_thresh_us, it's automatically marked
          * CPU_INTENSIVE to avoid stalling other concurrency-managed work items.
          *
          * Set @worker->sleeping means that @worker is in the process of
          * switching out voluntarily and won't be contributing to
          * @pool->nr_running until it wakes up. As wq_worker_sleeping() also
          * decrements ->nr_running, setting CPU_INTENSIVE here can lead to
          * double decrements. The task is releasing the CPU anyway. Let's skip.
          * We probably want to make this prettier in the future.
          */
         if ((worker->flags & WORKER_NOT_RUNNING) || READ_ONCE(worker->sleeping) ||
             worker->task->se.sum_exec_runtime - worker->current_at <
             wq_cpu_intensive_thresh_us * NSEC_PER_USEC)
                 return;
 
         raw_spin_lock(&pool->lock);
 
         worker_set_flags(worker, WORKER_CPU_INTENSIVE);
         wq_cpu_intensive_report(worker->current_func);
         pwq->stats[PWQ_STAT_CPU_INTENSIVE]++;
 
         if (kick_pool(pool))
                 pwq->stats[PWQ_STAT_CM_WAKEUP]++;
 
         raw_spin_unlock(&pool->lock);
 }
 
 /**
  * wq_worker_last_func - retrieve worker's last work function
  * @task: Task to retrieve last work function of.
  *
  * Determine the last function a worker executed. This is called from
  * the scheduler to get a worker's last known identity.
  *
  * CONTEXT:
  * raw_spin_lock_irq(rq->lock)
  *
  * This function is called during schedule() when a kworker is going
  * to sleep. It's used by psi to identify aggregation workers during
  * dequeuing, to allow periodic aggregation to shut-off when that
  * worker is the last task in the system or cgroup to go to sleep.
  *
  * As this function doesn't involve any workqueue-related locking, it
  * only returns stable values when called from inside the scheduler's
  * queuing and dequeuing paths, when @task, which must be a kworker,
  * is guaranteed to not be processing any works.
  *
  * Return:
  * The last work function %current executed as a worker, NULL if it
  * hasn't executed any work yet.
  */
 work_func_t wq_worker_last_func(struct task_struct *task)
 {
         struct worker *worker = kthread_data(task);
 
         return worker->last_func;
 }
 
 /**
  * wq_node_nr_active - Determine wq_node_nr_active to use
  * @wq: workqueue of interest
  * @node: NUMA node, can be %NUMA_NO_NODE
  *
  * Determine wq_node_nr_active to use for @wq on @node. Returns:
  *
  * - %NULL for per-cpu workqueues as they don't need to use shared nr_active.
  *
  * - node_nr_active[nr_node_ids] if @node is %NUMA_NO_NODE.
  *
  * - Otherwise, node_nr_active[@node].
  */
 static struct wq_node_nr_active *wq_node_nr_active(struct workqueue_struct *wq,
                                                    int node)
 {
         if (!(wq->flags & WQ_UNBOUND))
                 return NULL;
 
         if (node == NUMA_NO_NODE)
                 node = nr_node_ids;
 
         return wq->node_nr_active[node];
 }
 
 /**
  * wq_update_node_max_active - Update per-node max_actives to use
  * @wq: workqueue to update
  * @off_cpu: CPU that's going down, -1 if a CPU is not going down
  *
  * Update @wq->node_nr_active[]->max. @wq must be unbound. max_active is
  * distributed among nodes according to the proportions of numbers of online
  * cpus. The result is always between @wq->min_active and max_active.
  */
 static void wq_update_node_max_active(struct workqueue_struct *wq, int off_cpu)
 {
         struct cpumask *effective = unbound_effective_cpumask(wq);
         int min_active = READ_ONCE(wq->min_active);
         int max_active = READ_ONCE(wq->max_active);
         int total_cpus, node;
 
         lockdep_assert_held(&wq->mutex);
 
         if (!wq_topo_initialized)
                 return;
 
         if (off_cpu >= 0 && !cpumask_test_cpu(off_cpu, effective))
                 off_cpu = -1;
 
         total_cpus = cpumask_weight_and(effective, cpu_online_mask);
         if (off_cpu >= 0)
                 total_cpus--;
 
         /* If all CPUs of the wq get offline, use the default values */
         if (unlikely(!total_cpus)) {
                 for_each_node(node)
                         wq_node_nr_active(wq, node)->max = min_active;
 
                 wq_node_nr_active(wq, NUMA_NO_NODE)->max = max_active;
                 return;
         }
 
         for_each_node(node) {
                 int node_cpus;
 
                 node_cpus = cpumask_weight_and(effective, cpumask_of_node(node));
                 if (off_cpu >= 0 && cpu_to_node(off_cpu) == node)
                         node_cpus--;
 
                 wq_node_nr_active(wq, node)->max =
                         clamp(DIV_ROUND_UP(max_active * node_cpus, total_cpus),
                               min_active, max_active);
         }
 
         wq_node_nr_active(wq, NUMA_NO_NODE)->max = max_active;
 }
 
 /**
  * get_pwq - get an extra reference on the specified pool_workqueue
  * @pwq: pool_workqueue to get
  *
  * Obtain an extra reference on @pwq.  The caller should guarantee that
  * @pwq has positive refcnt and be holding the matching pool->lock.
  */
 static void get_pwq(struct pool_workqueue *pwq)
 {
         lockdep_assert_held(&pwq->pool->lock);
         WARN_ON_ONCE(pwq->refcnt <= 0);
         pwq->refcnt++;
 }
 
 /**
  * put_pwq - put a pool_workqueue reference
  * @pwq: pool_workqueue to put
  *
  * Drop a reference of @pwq.  If its refcnt reaches zero, schedule its
  * destruction.  The caller should be holding the matching pool->lock.
  */
 static void put_pwq(struct pool_workqueue *pwq)
 {
         lockdep_assert_held(&pwq->pool->lock);
         if (likely(--pwq->refcnt))
                 return;
         /*
          * @pwq can't be released under pool->lock, bounce to a dedicated
          * kthread_worker to avoid A-A deadlocks.
          */
         kthread_queue_work(pwq_release_worker, &pwq->release_work);
 }
 
 /**
  * put_pwq_unlocked - put_pwq() with surrounding pool lock/unlock
  * @pwq: pool_workqueue to put (can be %NULL)
  *
  * put_pwq() with locking.  This function also allows %NULL @pwq.
  */
 static void put_pwq_unlocked(struct pool_workqueue *pwq)
 {
         if (pwq) {
                 /*
                  * As both pwqs and pools are RCU protected, the
                  * following lock operations are safe.
                  */
                 raw_spin_lock_irq(&pwq->pool->lock);
                 put_pwq(pwq);
                 raw_spin_unlock_irq(&pwq->pool->lock);
         }
 }
 
 static bool pwq_is_empty(struct pool_workqueue *pwq)
 {
         return !pwq->nr_active && list_empty(&pwq->inactive_works);
 }
 
 static void __pwq_activate_work(struct pool_workqueue *pwq,
                                 struct work_struct *work)
 {
         unsigned long *wdb = work_data_bits(work);
 
         WARN_ON_ONCE(!(*wdb & WORK_STRUCT_INACTIVE));
         trace_workqueue_activate_work(work);
         if (list_empty(&pwq->pool->worklist))
                 pwq->pool->watchdog_ts = jiffies;
         move_linked_works(work, &pwq->pool->worklist, NULL);
         __clear_bit(WORK_STRUCT_INACTIVE_BIT, wdb);
 }
 
 static bool tryinc_node_nr_active(struct wq_node_nr_active *nna)
 {
         int max = READ_ONCE(nna->max);
 
         while (true) {
                 int old, tmp;
 
                 old = atomic_read(&nna->nr);
                 if (old >= max)
                         return false;
                 tmp = atomic_cmpxchg_relaxed(&nna->nr, old, old + 1);
                 if (tmp == old)
                         return true;
         }
 }
 
 /**
  * pwq_tryinc_nr_active - Try to increment nr_active for a pwq
  * @pwq: pool_workqueue of interest
  * @fill: max_active may have increased, try to increase concurrency level
  *
  * Try to increment nr_active for @pwq. Returns %true if an nr_active count is
  * successfully obtained. %false otherwise.
  */
 static bool pwq_tryinc_nr_active(struct pool_workqueue *pwq, bool fill)
 {
         struct workqueue_struct *wq = pwq->wq;
         struct worker_pool *pool = pwq->pool;
         struct wq_node_nr_active *nna = wq_node_nr_active(wq, pool->node);
         bool obtained = false;
 
         lockdep_assert_held(&pool->lock);
 
         if (!nna) {
                 /* BH or per-cpu workqueue, pwq->nr_active is sufficient */
                 obtained = pwq->nr_active < READ_ONCE(wq->max_active);
                 goto out;
         }
 
         if (unlikely(pwq->plugged))
                 return false;
 
         /*
          * Unbound workqueue uses per-node shared nr_active $nna. If @pwq is
          * already waiting on $nna, pwq_dec_nr_active() will maintain the
          * concurrency level. Don't jump the line.
          *
          * We need to ignore the pending test after max_active has increased as
          * pwq_dec_nr_active() can only maintain the concurrency level but not
          * increase it. This is indicated by @fill.
          */
         if (!list_empty(&pwq->pending_node) && likely(!fill))
                 goto out;
 
         obtained = tryinc_node_nr_active(nna);
         if (obtained)
                 goto out;
 
         /*
          * Lockless acquisition failed. Lock, add ourself to $nna->pending_pwqs
          * and try again. The smp_mb() is paired with the implied memory barrier
          * of atomic_dec_return() in pwq_dec_nr_active() to ensure that either
          * we see the decremented $nna->nr or they see non-empty
          * $nna->pending_pwqs.
          */
         raw_spin_lock(&nna->lock);
 
         if (list_empty(&pwq->pending_node))
                 list_add_tail(&pwq->pending_node, &nna->pending_pwqs);
         else if (likely(!fill))
                 goto out_unlock;
 
         smp_mb();
 
         obtained = tryinc_node_nr_active(nna);
 
         /*
          * If @fill, @pwq might have already been pending. Being spuriously
          * pending in cold paths doesn't affect anything. Let's leave it be.
          */
         if (obtained && likely(!fill))
                 list_del_init(&pwq->pending_node);
 
 out_unlock:
         raw_spin_unlock(&nna->lock);
 out:
         if (obtained)
                 pwq->nr_active++;
         return obtained;
 }
 
 /**
  * pwq_activate_first_inactive - Activate the first inactive work item on a pwq
  * @pwq: pool_workqueue of interest
  * @fill: max_active may have increased, try to increase concurrency level
  *
  * Activate the first inactive work item of @pwq if available and allowed by
  * max_active limit.
  *
  * Returns %true if an inactive work item has been activated. %false if no
  * inactive work item is found or max_active limit is reached.
  */
 static bool pwq_activate_first_inactive(struct pool_workqueue *pwq, bool fill)
 {
         struct work_struct *work =
                 list_first_entry_or_null(&pwq->inactive_works,
                                          struct work_struct, entry);
 
         if (work && pwq_tryinc_nr_active(pwq, fill)) {
                 __pwq_activate_work(pwq, work);
                 return true;
         } else {
                 return false;
         }
 }
 
 /**
  * unplug_oldest_pwq - unplug the oldest pool_workqueue
  * @wq: workqueue_struct where its oldest pwq is to be unplugged
  *
  * This function should only be called for ordered workqueues where only the
  * oldest pwq is unplugged, the others are plugged to suspend execution to
  * ensure proper work item ordering::
  *
  *    dfl_pwq --------------+     [P] - plugged
  *                          |
  *                          v
  *    pwqs -> A -> B [P] -> C [P] (newest)
  *            |    |        |
  *            1    3        5
  *            |    |        |
  *            2    4        6
  *
  * When the oldest pwq is drained and removed, this function should be called
  * to unplug the next oldest one to start its work item execution. Note that
  * pwq's are linked into wq->pwqs with the oldest first, so the first one in
  * the list is the oldest.
  */
 static void unplug_oldest_pwq(struct workqueue_struct *wq)
 {
         struct pool_workqueue *pwq;
 
         lockdep_assert_held(&wq->mutex);
 
         /* Caller should make sure that pwqs isn't empty before calling */
         pwq = list_first_entry_or_null(&wq->pwqs, struct pool_workqueue,
                                        pwqs_node);
         raw_spin_lock_irq(&pwq->pool->lock);
         if (pwq->plugged) {
                 pwq->plugged = false;
                 if (pwq_activate_first_inactive(pwq, true))
                         kick_pool(pwq->pool);
         }
         raw_spin_unlock_irq(&pwq->pool->lock);
 }
 
 /**
  * node_activate_pending_pwq - Activate a pending pwq on a wq_node_nr_active
  * @nna: wq_node_nr_active to activate a pending pwq for
  * @caller_pool: worker_pool the caller is locking
  *
  * Activate a pwq in @nna->pending_pwqs. Called with @caller_pool locked.
  * @caller_pool may be unlocked and relocked to lock other worker_pools.
  */
 static void node_activate_pending_pwq(struct wq_node_nr_active *nna,
                                       struct worker_pool *caller_pool)
 {
         struct worker_pool *locked_pool = caller_pool;
         struct pool_workqueue *pwq;
         struct work_struct *work;
 
         lockdep_assert_held(&caller_pool->lock);
 
         raw_spin_lock(&nna->lock);
 retry:
         pwq = list_first_entry_or_null(&nna->pending_pwqs,
                                        struct pool_workqueue, pending_node);
         if (!pwq)
                 goto out_unlock;
 
         /*
          * If @pwq is for a different pool than @locked_pool, we need to lock
          * @pwq->pool->lock. Let's trylock first. If unsuccessful, do the unlock
          * / lock dance. For that, we also need to release @nna->lock as it's
          * nested inside pool locks.
          */
         if (pwq->pool != locked_pool) {
                 raw_spin_unlock(&locked_pool->lock);
                 locked_pool = pwq->pool;
                 if (!raw_spin_trylock(&locked_pool->lock)) {
                         raw_spin_unlock(&nna->lock);
                         raw_spin_lock(&locked_pool->lock);
                         raw_spin_lock(&nna->lock);
                         goto retry;
                 }
         }
 
         /*
          * $pwq may not have any inactive work items due to e.g. cancellations.
          * Drop it from pending_pwqs and see if there's another one.
          */
         work = list_first_entry_or_null(&pwq->inactive_works,
                                         struct work_struct, entry);
         if (!work) {
                 list_del_init(&pwq->pending_node);
                 goto retry;
         }
 
         /*
          * Acquire an nr_active count and activate the inactive work item. If
          * $pwq still has inactive work items, rotate it to the end of the
          * pending_pwqs so that we round-robin through them. This means that
          * inactive work items are not activated in queueing order which is fine
          * given that there has never been any ordering across different pwqs.
          */
         if (likely(tryinc_node_nr_active(nna))) {
                 pwq->nr_active++;
                 __pwq_activate_work(pwq, work);
 
                 if (list_empty(&pwq->inactive_works))
                         list_del_init(&pwq->pending_node);
                 else
                         list_move_tail(&pwq->pending_node, &nna->pending_pwqs);
 
                 /* if activating a foreign pool, make sure it's running */
                 if (pwq->pool != caller_pool)
                         kick_pool(pwq->pool);
         }
 
 out_unlock:
         raw_spin_unlock(&nna->lock);
         if (locked_pool != caller_pool) {
                 raw_spin_unlock(&locked_pool->lock);
                 raw_spin_lock(&caller_pool->lock);
         }
 }
 
 /**
  * pwq_dec_nr_active - Retire an active count
  * @pwq: pool_workqueue of interest
  *
  * Decrement @pwq's nr_active and try to activate the first inactive work item.
  * For unbound workqueues, this function may temporarily drop @pwq->pool->lock.
  */
 static void pwq_dec_nr_active(struct pool_workqueue *pwq)
 {
         struct worker_pool *pool = pwq->pool;
         struct wq_node_nr_active *nna = wq_node_nr_active(pwq->wq, pool->node);
 
         lockdep_assert_held(&pool->lock);
 
         /*
          * @pwq->nr_active should be decremented for both percpu and unbound
          * workqueues.
          */
         pwq->nr_active--;
 
         /*
          * For a percpu workqueue, it's simple. Just need to kick the first
          * inactive work item on @pwq itself.
          */
         if (!nna) {
                 pwq_activate_first_inactive(pwq, false);
                 return;
         }
 
         /*
          * If @pwq is for an unbound workqueue, it's more complicated because
          * multiple pwqs and pools may be sharing the nr_active count. When a
          * pwq needs to wait for an nr_active count, it puts itself on
          * $nna->pending_pwqs. The following atomic_dec_return()'s implied
          * memory barrier is paired with smp_mb() in pwq_tryinc_nr_active() to
          * guarantee that either we see non-empty pending_pwqs or they see
          * decremented $nna->nr.
          *
          * $nna->max may change as CPUs come online/offline and @pwq->wq's
          * max_active gets updated. However, it is guaranteed to be equal to or
          * larger than @pwq->wq->min_active which is above zero unless freezing.
          * This maintains the forward progress guarantee.
          */
         if (atomic_dec_return(&nna->nr) >= READ_ONCE(nna->max))
                 return;
 
         if (!list_empty(&nna->pending_pwqs))
                 node_activate_pending_pwq(nna, pool);
 }
 
 /**
  * pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
  * @pwq: pwq of interest
  * @work_data: work_data of work which left the queue
  *
  * A work either has completed or is removed from pending queue,
  * decrement nr_in_flight of its pwq and handle workqueue flushing.
  *
  * NOTE:
  * For unbound workqueues, this function may temporarily drop @pwq->pool->lock
  * and thus should be called after all other state updates for the in-flight
  * work item is complete.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_data)
 {
         int color = get_work_color(work_data);
 
         if (!(work_data & WORK_STRUCT_INACTIVE))
                 pwq_dec_nr_active(pwq);
 
         pwq->nr_in_flight[color]--;
 
         /* is flush in progress and are we at the flushing tip? */
         if (likely(pwq->flush_color != color))
                 goto out_put;
 
         /* are there still in-flight works? */
         if (pwq->nr_in_flight[color])
                 goto out_put;
 
         /* this pwq is done, clear flush_color */
         pwq->flush_color = -1;
 
         /*
          * If this was the last pwq, wake up the first flusher.  It
          * will handle the rest.
          */
         if (atomic_dec_and_test(&pwq->wq->nr_pwqs_to_flush))
                 complete(&pwq->wq->first_flusher->done);
 out_put:
         put_pwq(pwq);
 }
 
 /**
  * try_to_grab_pending - steal work item from worklist and disable irq
  * @work: work item to steal
  * @cflags: %WORK_CANCEL_ flags
  * @irq_flags: place to store irq state
  *
  * Try to grab PENDING bit of @work.  This function can handle @work in any
  * stable state - idle, on timer or on worklist.
  *
  * Return:
  *
  *  ========    ================================================================
  *  1           if @work was pending and we successfully stole PENDING
  *  0           if @work was idle and we claimed PENDING
  *  -EAGAIN     if PENDING couldn't be grabbed at the moment, safe to busy-retry
  *  ========    ================================================================
  *
  * Note:
  * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting
  * interrupted while holding PENDING and @work off queue, irq must be
  * disabled on entry.  This, combined with delayed_work->timer being
  * irqsafe, ensures that we return -EAGAIN for finite short period of time.
  *
  * On successful return, >= 0, irq is disabled and the caller is
  * responsible for releasing it using local_irq_restore(*@irq_flags).
  *
  * This function is safe to call from any context including IRQ handler.
  */
 static int try_to_grab_pending(struct work_struct *work, u32 cflags,
                                unsigned long *irq_flags)
 {
         struct worker_pool *pool;
         struct pool_workqueue *pwq;
 
         local_irq_save(*irq_flags);
 
         /* try to steal the timer if it exists */
         if (cflags & WORK_CANCEL_DELAYED) {
                 struct delayed_work *dwork = to_delayed_work(work);
 
                 /*
                  * dwork->timer is irqsafe.  If del_timer() fails, it's
                  * guaranteed that the timer is not queued anywhere and not
                  * running on the local CPU.
                  */
                 if (likely(del_timer(&dwork->timer)))
                         return 1;
         }
 
         /* try to claim PENDING the normal way */
         if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
                 return 0;
 
         rcu_read_lock();
         /*
          * The queueing is in progress, or it is already queued. Try to
          * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
          */
         pool = get_work_pool(work);
         if (!pool)
                 goto fail;
 
         raw_spin_lock(&pool->lock);
         /*
          * work->data is guaranteed to point to pwq only while the work
          * item is queued on pwq->wq, and both updating work->data to point
          * to pwq on queueing and to pool on dequeueing are done under
          * pwq->pool->lock.  This in turn guarantees that, if work->data
          * points to pwq which is associated with a locked pool, the work
          * item is currently queued on that pool.
          */
         pwq = get_work_pwq(work);
         if (pwq && pwq->pool == pool) {
                 unsigned long work_data = *work_data_bits(work);
 
                 debug_work_deactivate(work);
 
                 /*
                  * A cancelable inactive work item must be in the
                  * pwq->inactive_works since a queued barrier can't be
                  * canceled (see the comments in insert_wq_barrier()).
                  *
                  * An inactive work item cannot be deleted directly because
                  * it might have linked barrier work items which, if left
                  * on the inactive_works list, will confuse pwq->nr_active
                  * management later on and cause stall.  Move the linked
                  * barrier work items to the worklist when deleting the grabbed
                  * item. Also keep WORK_STRUCT_INACTIVE in work_data, so that
                  * it doesn't participate in nr_active management in later
                  * pwq_dec_nr_in_flight().
                  */
                 if (work_data & WORK_STRUCT_INACTIVE)
                         move_linked_works(work, &pwq->pool->worklist, NULL);
 
                 list_del_init(&work->entry);
 
                 /*
                  * work->data points to pwq iff queued. Let's point to pool. As
                  * this destroys work->data needed by the next step, stash it.
                  */
                 set_work_pool_and_keep_pending(work, pool->id,
                                                pool_offq_flags(pool));
 
                 /* must be the last step, see the function comment */
                 pwq_dec_nr_in_flight(pwq, work_data);
 
                 raw_spin_unlock(&pool->lock);
                 rcu_read_unlock();
                 return 1;
         }
         raw_spin_unlock(&pool->lock);
 fail:
         rcu_read_unlock();
         local_irq_restore(*irq_flags);
         return -EAGAIN;
 }
 
 /**
  * work_grab_pending - steal work item from worklist and disable irq
  * @work: work item to steal
  * @cflags: %WORK_CANCEL_ flags
  * @irq_flags: place to store IRQ state
  *
  * Grab PENDING bit of @work. @work can be in any stable state - idle, on timer
  * or on worklist.
  *
  * Can be called from any context. IRQ is disabled on return with IRQ state
  * stored in *@irq_flags. The caller is responsible for re-enabling it using
  * local_irq_restore().
  *
  * Returns %true if @work was pending. %false if idle.
  */
 static bool work_grab_pending(struct work_struct *work, u32 cflags,
                               unsigned long *irq_flags)
 {
         int ret;
 
         while (true) {
                 ret = try_to_grab_pending(work, cflags, irq_flags);
                 if (ret >= 0)
                         return ret;
                 cpu_relax();
         }
 }
 
 /**
  * insert_work - insert a work into a pool
  * @pwq: pwq @work belongs to
  * @work: work to insert
  * @head: insertion point
  * @extra_flags: extra WORK_STRUCT_* flags to set
  *
  * Insert @work which belongs to @pwq after @head.  @extra_flags is or'd to
  * work_struct flags.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
                         struct list_head *head, unsigned int extra_flags)
 {
         debug_work_activate(work);
 
         /* record the work call stack in order to print it in KASAN reports */
         kasan_record_aux_stack_noalloc(work);
 
         /* we own @work, set data and link */
         set_work_pwq(work, pwq, extra_flags);
         list_add_tail(&work->entry, head);
         get_pwq(pwq);
 }
 
 /*
  * Test whether @work is being queued from another work executing on the
  * same workqueue.
  */
 static bool is_chained_work(struct workqueue_struct *wq)
 {
         struct worker *worker;
 
         worker = current_wq_worker();
         /*
          * Return %true iff I'm a worker executing a work item on @wq.  If
          * I'm @worker, it's safe to dereference it without locking.
          */
         return worker && worker->current_pwq->wq == wq;
 }
 
 /*
  * When queueing an unbound work item to a wq, prefer local CPU if allowed
  * by wq_unbound_cpumask.  Otherwise, round robin among the allowed ones to
  * avoid perturbing sensitive tasks.
  */
 static int wq_select_unbound_cpu(int cpu)
 {
         int new_cpu;
 
         if (likely(!wq_debug_force_rr_cpu)) {
                 if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
                         return cpu;
         } else {
                 pr_warn_once("workqueue: round-robin CPU selection forced, expect performance impact\n");
         }
 
         new_cpu = __this_cpu_read(wq_rr_cpu_last);
         new_cpu = cpumask_next_and(new_cpu, wq_unbound_cpumask, cpu_online_mask);
         if (unlikely(new_cpu >= nr_cpu_ids)) {
                 new_cpu = cpumask_first_and(wq_unbound_cpumask, cpu_online_mask);
                 if (unlikely(new_cpu >= nr_cpu_ids))
                         return cpu;
         }
         __this_cpu_write(wq_rr_cpu_last, new_cpu);
 
         return new_cpu;
 }
 
 static void __queue_work(int cpu, struct workqueue_struct *wq,
                          struct work_struct *work)
 {
         struct pool_workqueue *pwq;
         struct worker_pool *last_pool, *pool;
         unsigned int work_flags;
         unsigned int req_cpu = cpu;
 
         /*
          * While a work item is PENDING && off queue, a task trying to
          * steal the PENDING will busy-loop waiting for it to either get
          * queued or lose PENDING.  Grabbing PENDING and queueing should
          * happen with IRQ disabled.
          */
         lockdep_assert_irqs_disabled();
 
         /*
          * For a draining wq, only works from the same workqueue are
          * allowed. The __WQ_DESTROYING helps to spot the issue that
          * queues a new work item to a wq after destroy_workqueue(wq).
          */
         if (unlikely(wq->flags & (__WQ_DESTROYING | __WQ_DRAINING) &&
                      WARN_ON_ONCE(!is_chained_work(wq))))
                 return;
         rcu_read_lock();
 retry:
         /* pwq which will be used unless @work is executing elsewhere */
         if (req_cpu == WORK_CPU_UNBOUND) {
                 if (wq->flags & WQ_UNBOUND)
                         cpu = wq_select_unbound_cpu(raw_smp_processor_id());
                 else
                         cpu = raw_smp_processor_id();
         }
 
         pwq = rcu_dereference(*per_cpu_ptr(wq->cpu_pwq, cpu));
         pool = pwq->pool;
 
         /*
          * If @work was previously on a different pool, it might still be
          * running there, in which case the work needs to be queued on that
          * pool to guarantee non-reentrancy.
          *
          * For ordered workqueue, work items must be queued on the newest pwq
          * for accurate order management.  Guaranteed order also guarantees
          * non-reentrancy.  See the comments above unplug_oldest_pwq().
          */
         last_pool = get_work_pool(work);
         if (last_pool && last_pool != pool && !(wq->flags & __WQ_ORDERED)) {
                 struct worker *worker;
 
                 raw_spin_lock(&last_pool->lock);
 
                 worker = find_worker_executing_work(last_pool, work);
 
                 if (worker && worker->current_pwq->wq == wq) {
                         pwq = worker->current_pwq;
                         pool = pwq->pool;
                         WARN_ON_ONCE(pool != last_pool);
                 } else {
                         /* meh... not running there, queue here */
                         raw_spin_unlock(&last_pool->lock);
                         raw_spin_lock(&pool->lock);
                 }
         } else {
                 raw_spin_lock(&pool->lock);
         }
 
         /*
          * pwq is determined and locked. For unbound pools, we could have raced
          * with pwq release and it could already be dead. If its refcnt is zero,
          * repeat pwq selection. Note that unbound pwqs never die without
          * another pwq replacing it in cpu_pwq or while work items are executing
          * on it, so the retrying is guaranteed to make forward-progress.
          */
         if (unlikely(!pwq->refcnt)) {
                 if (wq->flags & WQ_UNBOUND) {
                         raw_spin_unlock(&pool->lock);
                         cpu_relax();
                         goto retry;
                 }
                 /* oops */
                 WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
                           wq->name, cpu);
         }
 
         /* pwq determined, queue */
         trace_workqueue_queue_work(req_cpu, pwq, work);
 
         if (WARN_ON(!list_empty(&work->entry)))
                 goto out;
 
         pwq->nr_in_flight[pwq->work_color]++;
         work_flags = work_color_to_flags(pwq->work_color);
 
         /*
          * Limit the number of concurrently active work items to max_active.
          * @work must also queue behind existing inactive work items to maintain
          * ordering when max_active changes. See wq_adjust_max_active().
          */
         if (list_empty(&pwq->inactive_works) && pwq_tryinc_nr_active(pwq, false)) {
                 if (list_empty(&pool->worklist))
                         pool->watchdog_ts = jiffies;
 
                 trace_workqueue_activate_work(work);
                 insert_work(pwq, work, &pool->worklist, work_flags);
                 kick_pool(pool);
         } else {
                 work_flags |= WORK_STRUCT_INACTIVE;
                 insert_work(pwq, work, &pwq->inactive_works, work_flags);
         }
 
 out:
         raw_spin_unlock(&pool->lock);
         rcu_read_unlock();
 }
 
 static bool clear_pending_if_disabled(struct work_struct *work)
 {
         unsigned long data = *work_data_bits(work);
         struct work_offq_data offqd;
 
         if (likely((data & WORK_STRUCT_PWQ) ||
                    !(data & WORK_OFFQ_DISABLE_MASK)))
                 return false;
 
         work_offqd_unpack(&offqd, data);
         set_work_pool_and_clear_pending(work, offqd.pool_id,
                                         work_offqd_pack_flags(&offqd));
         return true;
 }
 
 /**
  * queue_work_on - queue work on specific cpu
  * @cpu: CPU number to execute work on
  * @wq: workqueue to use
  * @work: work to queue
  *
  * We queue the work to a specific CPU, the caller must ensure it
  * can't go away.  Callers that fail to ensure that the specified
  * CPU cannot go away will execute on a randomly chosen CPU.
  * But note well that callers specifying a CPU that never has been
  * online will get a splat.
  *
  * Return: %false if @work was already on a queue, %true otherwise.
  */
 bool queue_work_on(int cpu, struct workqueue_struct *wq,
                    struct work_struct *work)
 {
         bool ret = false;
         unsigned long irq_flags;
 
         local_irq_save(irq_flags);
 
         if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
             !clear_pending_if_disabled(work)) {
                 __queue_work(cpu, wq, work);
                 ret = true;
         }
 
         local_irq_restore(irq_flags);
         return ret;
 }
 EXPORT_SYMBOL(queue_work_on);
 
 /**
  * select_numa_node_cpu - Select a CPU based on NUMA node
  * @node: NUMA node ID that we want to select a CPU from
  *
  * This function will attempt to find a "random" cpu available on a given
  * node. If there are no CPUs available on the given node it will return
  * WORK_CPU_UNBOUND indicating that we should just schedule to any
  * available CPU if we need to schedule this work.
  */
 static int select_numa_node_cpu(int node)
 {
         int cpu;
 
         /* Delay binding to CPU if node is not valid or online */
         if (node < 0 || node >= MAX_NUMNODES || !node_online(node))
                 return WORK_CPU_UNBOUND;
 
         /* Use local node/cpu if we are already there */
         cpu = raw_smp_processor_id();
         if (node == cpu_to_node(cpu))
                 return cpu;
 
         /* Use "random" otherwise know as "first" online CPU of node */
         cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
 
         /* If CPU is valid return that, otherwise just defer */
         return cpu < nr_cpu_ids ? cpu : WORK_CPU_UNBOUND;
 }
 
 /**
  * queue_work_node - queue work on a "random" cpu for a given NUMA node
  * @node: NUMA node that we are targeting the work for
  * @wq: workqueue to use
  * @work: work to queue
  *
  * We queue the work to a "random" CPU within a given NUMA node. The basic
  * idea here is to provide a way to somehow associate work with a given
  * NUMA node.
  *
  * This function will only make a best effort attempt at getting this onto
  * the right NUMA node. If no node is requested or the requested node is
  * offline then we just fall back to standard queue_work behavior.
  *
  * Currently the "random" CPU ends up being the first available CPU in the
  * intersection of cpu_online_mask and the cpumask of the node, unless we
  * are running on the node. In that case we just use the current CPU.
  *
  * Return: %false if @work was already on a queue, %true otherwise.
  */
 bool queue_work_node(int node, struct workqueue_struct *wq,
                      struct work_struct *work)
 {
         unsigned long irq_flags;
         bool ret = false;
 
         /*
          * This current implementation is specific to unbound workqueues.
          * Specifically we only return the first available CPU for a given
          * node instead of cycling through individual CPUs within the node.
          *
          * If this is used with a per-cpu workqueue then the logic in
          * workqueue_select_cpu_near would need to be updated to allow for
          * some round robin type logic.
          */
         WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND));
 
         local_irq_save(irq_flags);
 
         if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
             !clear_pending_if_disabled(work)) {
                 int cpu = select_numa_node_cpu(node);
 
                 __queue_work(cpu, wq, work);
                 ret = true;
         }
 
         local_irq_restore(irq_flags);
         return ret;
 }
 EXPORT_SYMBOL_GPL(queue_work_node);
 
 void delayed_work_timer_fn(struct timer_list *t)
 {
         struct delayed_work *dwork = from_timer(dwork, t, timer);
 
         /* should have been called from irqsafe timer with irq already off */
         __queue_work(dwork->cpu, dwork->wq, &dwork->work);
 }
 EXPORT_SYMBOL(delayed_work_timer_fn);
 
 static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
                                 struct delayed_work *dwork, unsigned long delay)
 {
         struct timer_list *timer = &dwork->timer;
         struct work_struct *work = &dwork->work;
 
         WARN_ON_ONCE(!wq);
         WARN_ON_ONCE(timer->function != delayed_work_timer_fn);
         WARN_ON_ONCE(timer_pending(timer));
         WARN_ON_ONCE(!list_empty(&work->entry));
 
         /*
          * If @delay is 0, queue @dwork->work immediately.  This is for
          * both optimization and correctness.  The earliest @timer can
          * expire is on the closest next tick and delayed_work users depend
          * on that there's no such delay when @delay is 0.
          */
         if (!delay) {
                 __queue_work(cpu, wq, &dwork->work);
                 return;
         }
 
         dwork->wq = wq;
         dwork->cpu = cpu;
         timer->expires = jiffies + delay;
 
         if (housekeeping_enabled(HK_TYPE_TIMER)) {
                 /* If the current cpu is a housekeeping cpu, use it. */
                 cpu = smp_processor_id();
                 if (!housekeeping_test_cpu(cpu, HK_TYPE_TIMER))
                         cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
                 add_timer_on(timer, cpu);
         } else {
                 if (likely(cpu == WORK_CPU_UNBOUND))
                         add_timer_global(timer);
                 else
                         add_timer_on(timer, cpu);
         }
 }
 
 /**
  * queue_delayed_work_on - queue work on specific CPU after delay
  * @cpu: CPU number to execute work on
  * @wq: workqueue to use
  * @dwork: work to queue
  * @delay: number of jiffies to wait before queueing
  *
  * Return: %false if @work was already on a queue, %true otherwise.  If
  * @delay is zero and @dwork is idle, it will be scheduled for immediate
  * execution.
  */
 bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
                            struct delayed_work *dwork, unsigned long delay)
 {
         struct work_struct *work = &dwork->work;
         bool ret = false;
         unsigned long irq_flags;
 
         /* read the comment in __queue_work() */
         local_irq_save(irq_flags);
 
         if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
             !clear_pending_if_disabled(work)) {
                 __queue_delayed_work(cpu, wq, dwork, delay);
                 ret = true;
         }
 
         local_irq_restore(irq_flags);
         return ret;
 }
 EXPORT_SYMBOL(queue_delayed_work_on);
 
 /**
  * mod_delayed_work_on - modify delay of or queue a delayed work on specific CPU
  * @cpu: CPU number to execute work on
  * @wq: workqueue to use
  * @dwork: work to queue
  * @delay: number of jiffies to wait before queueing
  *
  * If @dwork is idle, equivalent to queue_delayed_work_on(); otherwise,
  * modify @dwork's timer so that it expires after @delay.  If @delay is
  * zero, @work is guaranteed to be scheduled immediately regardless of its
  * current state.
  *
  * Return: %false if @dwork was idle and queued, %true if @dwork was
  * pending and its timer was modified.
  *
  * This function is safe to call from any context including IRQ handler.
  * See try_to_grab_pending() for details.
  */
 bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
                          struct delayed_work *dwork, unsigned long delay)
 {
         unsigned long irq_flags;
         bool ret;
 
         ret = work_grab_pending(&dwork->work, WORK_CANCEL_DELAYED, &irq_flags);
 
         if (!clear_pending_if_disabled(&dwork->work))
                 __queue_delayed_work(cpu, wq, dwork, delay);
 
         local_irq_restore(irq_flags);
         return ret;
 }
 EXPORT_SYMBOL_GPL(mod_delayed_work_on);
 
 static void rcu_work_rcufn(struct rcu_head *rcu)
 {
         struct rcu_work *rwork = container_of(rcu, struct rcu_work, rcu);
 
         /* read the comment in __queue_work() */
         local_irq_disable();
         __queue_work(WORK_CPU_UNBOUND, rwork->wq, &rwork->work);
         local_irq_enable();
 }
 
 /**
  * queue_rcu_work - queue work after a RCU grace period
  * @wq: workqueue to use
  * @rwork: work to queue
  *
  * Return: %false if @rwork was already pending, %true otherwise.  Note
  * that a full RCU grace period is guaranteed only after a %true return.
  * While @rwork is guaranteed to be executed after a %false return, the
  * execution may happen before a full RCU grace period has passed.
  */
 bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork)
 {
         struct work_struct *work = &rwork->work;
 
         /*
          * rcu_work can't be canceled or disabled. Warn if the user reached
          * inside @rwork and disabled the inner work.
          */
         if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
             !WARN_ON_ONCE(clear_pending_if_disabled(work))) {
                 rwork->wq = wq;
                 call_rcu_hurry(&rwork->rcu, rcu_work_rcufn);
                 return true;
         }
 
         return false;
 }
 EXPORT_SYMBOL(queue_rcu_work);
 
 static struct worker *alloc_worker(int node)
 {
         struct worker *worker;
 
         worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node);
         if (worker) {
                 INIT_LIST_HEAD(&worker->entry);
                 INIT_LIST_HEAD(&worker->scheduled);
                 INIT_LIST_HEAD(&worker->node);
                 /* on creation a worker is in !idle && prep state */
                 worker->flags = WORKER_PREP;
         }
         return worker;
 }
 
 static cpumask_t *pool_allowed_cpus(struct worker_pool *pool)
 {
         if (pool->cpu < 0 && pool->attrs->affn_strict)
                 return pool->attrs->__pod_cpumask;
         else
                 return pool->attrs->cpumask;
 }
 
 /**
  * worker_attach_to_pool() - attach a worker to a pool
  * @worker: worker to be attached
  * @pool: the target pool
  *
  * Attach @worker to @pool.  Once attached, the %WORKER_UNBOUND flag and
  * cpu-binding of @worker are kept coordinated with the pool across
  * cpu-[un]hotplugs.
  */
 static void worker_attach_to_pool(struct worker *worker,
                                   struct worker_pool *pool)
 {
         mutex_lock(&wq_pool_attach_mutex);
 
         /*
          * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains stable
          * across this function. See the comments above the flag definition for
          * details. BH workers are, while per-CPU, always DISASSOCIATED.
          */
         if (pool->flags & POOL_DISASSOCIATED) {
                 worker->flags |= WORKER_UNBOUND;
         } else {
                 WARN_ON_ONCE(pool->flags & POOL_BH);
                 kthread_set_per_cpu(worker->task, pool->cpu);
         }
 
         if (worker->rescue_wq)
                 set_cpus_allowed_ptr(worker->task, pool_allowed_cpus(pool));
 
         list_add_tail(&worker->node, &pool->workers);
         worker->pool = pool;
 
         mutex_unlock(&wq_pool_attach_mutex);
 }
 
 static void unbind_worker(struct worker *worker)
 {
         lockdep_assert_held(&wq_pool_attach_mutex);
 
         kthread_set_per_cpu(worker->task, -1);
         if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
         else
                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
 }
 
 
 static void detach_worker(struct worker *worker)
 {
         lockdep_assert_held(&wq_pool_attach_mutex);
 
         unbind_worker(worker);
         list_del(&worker->node);
         worker->pool = NULL;
 }
 
 /**
  * worker_detach_from_pool() - detach a worker from its pool
  * @worker: worker which is attached to its pool
  *
  * Undo the attaching which had been done in worker_attach_to_pool().  The
  * caller worker shouldn't access to the pool after detached except it has
  * other reference to the pool.
  */
 static void worker_detach_from_pool(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
 
         /* there is one permanent BH worker per CPU which should never detach */
         WARN_ON_ONCE(pool->flags & POOL_BH);
 
         mutex_lock(&wq_pool_attach_mutex);
         detach_worker(worker);
         mutex_unlock(&wq_pool_attach_mutex);
 
         /* clear leftover flags without pool->lock after it is detached */
         worker->flags &= ~(WORKER_UNBOUND | WORKER_REBOUND);
 }
 
 static int format_worker_id(char *buf, size_t size, struct worker *worker,
                             struct worker_pool *pool)
 {
         if (worker->rescue_wq)
                 return scnprintf(buf, size, "kworker/R-%s",
                                  worker->rescue_wq->name);
 
         if (pool) {
                 if (pool->cpu >= 0)
                         return scnprintf(buf, size, "kworker/%d:%d%s",
                                          pool->cpu, worker->id,
                                          pool->attrs->nice < 0  ? "H" : "");
                 else
                         return scnprintf(buf, size, "kworker/u%d:%d",
                                          pool->id, worker->id);
         } else {
                 return scnprintf(buf, size, "kworker/dying");
         }
 }
 
 /**
  * create_worker - create a new workqueue worker
  * @pool: pool the new worker will belong to
  *
  * Create and start a new worker which is attached to @pool.
  *
  * CONTEXT:
  * Might sleep.  Does GFP_KERNEL allocations.
  *
  * Return:
  * Pointer to the newly created worker.
  */
 static struct worker *create_worker(struct worker_pool *pool)
 {
         struct worker *worker;
         int id;
 
         /* ID is needed to determine kthread name */
         id = ida_alloc(&pool->worker_ida, GFP_KERNEL);
         if (id < 0) {
                 pr_err_once("workqueue: Failed to allocate a worker ID: %pe\n",
                             ERR_PTR(id));
                 return NULL;
         }
 
         worker = alloc_worker(pool->node);
         if (!worker) {
                 pr_err_once("workqueue: Failed to allocate a worker\n");
                 goto fail;
         }
 
         worker->id = id;
 
         if (!(pool->flags & POOL_BH)) {
                 char id_buf[WORKER_ID_LEN];
 
                 format_worker_id(id_buf, sizeof(id_buf), worker, pool);
                 worker->task = kthread_create_on_node(worker_thread, worker,
                                                       pool->node, "%s", id_buf);
                 if (IS_ERR(worker->task)) {
                         if (PTR_ERR(worker->task) == -EINTR) {
                                 pr_err("workqueue: Interrupted when creating a worker thread \"%s\"\n",
                                        id_buf);
                         } else {
                                 pr_err_once("workqueue: Failed to create a worker thread: %pe",
                                             worker->task);
                         }
                         goto fail;
                 }
 
                 set_user_nice(worker->task, pool->attrs->nice);
                 kthread_bind_mask(worker->task, pool_allowed_cpus(pool));
         }
 
         /* successful, attach the worker to the pool */
         worker_attach_to_pool(worker, pool);
 
         /* start the newly created worker */
         raw_spin_lock_irq(&pool->lock);
 
         worker->pool->nr_workers++;
         worker_enter_idle(worker);
 
         /*
          * @worker is waiting on a completion in kthread() and will trigger hung
          * check if not woken up soon. As kick_pool() is noop if @pool is empty,
          * wake it up explicitly.
          */
         if (worker->task)
                 wake_up_process(worker->task);
 
         raw_spin_unlock_irq(&pool->lock);
 
         return worker;
 
 fail:
         ida_free(&pool->worker_ida, id);
         kfree(worker);
         return NULL;
 }
 
 static void detach_dying_workers(struct list_head *cull_list)
 {
         struct worker *worker;
 
         list_for_each_entry(worker, cull_list, entry)
                 detach_worker(worker);
 }
 
 static void reap_dying_workers(struct list_head *cull_list)
 {
         struct worker *worker, *tmp;
 
         list_for_each_entry_safe(worker, tmp, cull_list, entry) {
                 list_del_init(&worker->entry);
                 kthread_stop_put(worker->task);
                 kfree(worker);
         }
 }
 
 /**
  * set_worker_dying - Tag a worker for destruction
  * @worker: worker to be destroyed
  * @list: transfer worker away from its pool->idle_list and into list
  *
  * Tag @worker for destruction and adjust @pool stats accordingly.  The worker
  * should be idle.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void set_worker_dying(struct worker *worker, struct list_head *list)
 {
         struct worker_pool *pool = worker->pool;
 
         lockdep_assert_held(&pool->lock);
         lockdep_assert_held(&wq_pool_attach_mutex);
 
         /* sanity check frenzy */
         if (WARN_ON(worker->current_work) ||
             WARN_ON(!list_empty(&worker->scheduled)) ||
             WARN_ON(!(worker->flags & WORKER_IDLE)))
                 return;
 
         pool->nr_workers--;
         pool->nr_idle--;
 
         worker->flags |= WORKER_DIE;
 
         list_move(&worker->entry, list);
 
         /* get an extra task struct reference for later kthread_stop_put() */
         get_task_struct(worker->task);
 }
 
 /**
  * idle_worker_timeout - check if some idle workers can now be deleted.
  * @t: The pool's idle_timer that just expired
  *
  * The timer is armed in worker_enter_idle(). Note that it isn't disarmed in
  * worker_leave_idle(), as a worker flicking between idle and active while its
  * pool is at the too_many_workers() tipping point would cause too much timer
  * housekeeping overhead. Since IDLE_WORKER_TIMEOUT is long enough, we just let
  * it expire and re-evaluate things from there.
  */
 static void idle_worker_timeout(struct timer_list *t)
 {
         struct worker_pool *pool = from_timer(pool, t, idle_timer);
         bool do_cull = false;
 
         if (work_pending(&pool->idle_cull_work))
                 return;
 
         raw_spin_lock_irq(&pool->lock);
 
         if (too_many_workers(pool)) {
                 struct worker *worker;
                 unsigned long expires;
 
                 /* idle_list is kept in LIFO order, check the last one */
                 worker = list_last_entry(&pool->idle_list, struct worker, entry);
                 expires = worker->last_active + IDLE_WORKER_TIMEOUT;
                 do_cull = !time_before(jiffies, expires);
 
                 if (!do_cull)
                         mod_timer(&pool->idle_timer, expires);
         }
         raw_spin_unlock_irq(&pool->lock);
 
         if (do_cull)
                 queue_work(system_unbound_wq, &pool->idle_cull_work);
 }
 
 /**
  * idle_cull_fn - cull workers that have been idle for too long.
  * @work: the pool's work for handling these idle workers
  *
  * This goes through a pool's idle workers and gets rid of those that have been
  * idle for at least IDLE_WORKER_TIMEOUT seconds.
  *
  * We don't want to disturb isolated CPUs because of a pcpu kworker being
  * culled, so this also resets worker affinity. This requires a sleepable
  * context, hence the split between timer callback and work item.
  */
 static void idle_cull_fn(struct work_struct *work)
 {
         struct worker_pool *pool = container_of(work, struct worker_pool, idle_cull_work);
         LIST_HEAD(cull_list);
 
         /*
          * Grabbing wq_pool_attach_mutex here ensures an already-running worker
          * cannot proceed beyong set_pf_worker() in its self-destruct path.
          * This is required as a previously-preempted worker could run after
          * set_worker_dying() has happened but before detach_dying_workers() did.
          */
         mutex_lock(&wq_pool_attach_mutex);
         raw_spin_lock_irq(&pool->lock);
 
         while (too_many_workers(pool)) {
                 struct worker *worker;
                 unsigned long expires;
 
                 worker = list_last_entry(&pool->idle_list, struct worker, entry);
                 expires = worker->last_active + IDLE_WORKER_TIMEOUT;
 
                 if (time_before(jiffies, expires)) {
                         mod_timer(&pool->idle_timer, expires);
                         break;
                 }
 
                 set_worker_dying(worker, &cull_list);
         }
 
         raw_spin_unlock_irq(&pool->lock);
         detach_dying_workers(&cull_list);
         mutex_unlock(&wq_pool_attach_mutex);
 
         reap_dying_workers(&cull_list);
 }
 
 static void send_mayday(struct work_struct *work)
 {
         struct pool_workqueue *pwq = get_work_pwq(work);
         struct workqueue_struct *wq = pwq->wq;
 
         lockdep_assert_held(&wq_mayday_lock);
 
         if (!wq->rescuer)
                 return;
 
         /* mayday mayday mayday */
         if (list_empty(&pwq->mayday_node)) {
                 /*
                  * If @pwq is for an unbound wq, its base ref may be put at
                  * any time due to an attribute change.  Pin @pwq until the
                  * rescuer is done with it.
                  */
                 get_pwq(pwq);
                 list_add_tail(&pwq->mayday_node, &wq->maydays);
                 wake_up_process(wq->rescuer->task);
                 pwq->stats[PWQ_STAT_MAYDAY]++;
         }
 }
 
 static void pool_mayday_timeout(struct timer_list *t)
 {
         struct worker_pool *pool = from_timer(pool, t, mayday_timer);
         struct work_struct *work;
 
         raw_spin_lock_irq(&pool->lock);
         raw_spin_lock(&wq_mayday_lock);         /* for wq->maydays */
 
         if (need_to_create_worker(pool)) {
                 /*
                  * We've been trying to create a new worker but
                  * haven't been successful.  We might be hitting an
                  * allocation deadlock.  Send distress signals to
                  * rescuers.
                  */
                 list_for_each_entry(work, &pool->worklist, entry)
                         send_mayday(work);
         }
 
         raw_spin_unlock(&wq_mayday_lock);
         raw_spin_unlock_irq(&pool->lock);
 
         mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
 }
 
 /**
  * maybe_create_worker - create a new worker if necessary
  * @pool: pool to create a new worker for
  *
  * Create a new worker for @pool if necessary.  @pool is guaranteed to
  * have at least one idle worker on return from this function.  If
  * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
  * sent to all rescuers with works scheduled on @pool to resolve
  * possible allocation deadlock.
  *
  * On return, need_to_create_worker() is guaranteed to be %false and
  * may_start_working() %true.
  *
  * LOCKING:
  * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.  Does GFP_KERNEL allocations.  Called only from
  * manager.
  */
 static void maybe_create_worker(struct worker_pool *pool)
 __releases(&pool->lock)
 __acquires(&pool->lock)
 {
 restart:
         raw_spin_unlock_irq(&pool->lock);
 
         /* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
         mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
 
         while (true) {
                 if (create_worker(pool) || !need_to_create_worker(pool))
                         break;
 
                 schedule_timeout_interruptible(CREATE_COOLDOWN);
 
                 if (!need_to_create_worker(pool))
                         break;
         }
 
         del_timer_sync(&pool->mayday_timer);
         raw_spin_lock_irq(&pool->lock);
         /*
          * This is necessary even after a new worker was just successfully
          * created as @pool->lock was dropped and the new worker might have
          * already become busy.
          */
         if (need_to_create_worker(pool))
                 goto restart;
 }
 
 /**
  * manage_workers - manage worker pool
  * @worker: self
  *
  * Assume the manager role and manage the worker pool @worker belongs
  * to.  At any given time, there can be only zero or one manager per
  * pool.  The exclusion is handled automatically by this function.
  *
  * The caller can safely start processing works on false return.  On
  * true return, it's guaranteed that need_to_create_worker() is false
  * and may_start_working() is true.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.  Does GFP_KERNEL allocations.
  *
  * Return:
  * %false if the pool doesn't need management and the caller can safely
  * start processing works, %true if management function was performed and
  * the conditions that the caller verified before calling the function may
  * no longer be true.
  */
 static bool manage_workers(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
 
         if (pool->flags & POOL_MANAGER_ACTIVE)
                 return false;
 
         pool->flags |= POOL_MANAGER_ACTIVE;
         pool->manager = worker;
 
         maybe_create_worker(pool);
 
         pool->manager = NULL;
         pool->flags &= ~POOL_MANAGER_ACTIVE;
         rcuwait_wake_up(&manager_wait);
         return true;
 }
 
 /**
  * process_one_work - process single work
  * @worker: self
  * @work: work to process
  *
  * Process @work.  This function contains all the logics necessary to
  * process a single work including synchronization against and
  * interaction with other workers on the same cpu, queueing and
  * flushing.  As long as context requirement is met, any worker can
  * call this function to process a work.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock) which is released and regrabbed.
  */
 static void process_one_work(struct worker *worker, struct work_struct *work)
 __releases(&pool->lock)
 __acquires(&pool->lock)
 {
         struct pool_workqueue *pwq = get_work_pwq(work);
         struct worker_pool *pool = worker->pool;
         unsigned long work_data;
         int lockdep_start_depth, rcu_start_depth;
         bool bh_draining = pool->flags & POOL_BH_DRAINING;
 #ifdef CONFIG_LOCKDEP
         /*
          * It is permissible to free the struct work_struct from
          * inside the function that is called from it, this we need to
          * take into account for lockdep too.  To avoid bogus "held
          * lock freed" warnings as well as problems when looking into
          * work->lockdep_map, make a copy and use that here.
          */
         struct lockdep_map lockdep_map;
 
         lockdep_copy_map(&lockdep_map, &work->lockdep_map);
 #endif
         /* ensure we're on the correct CPU */
         WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
                      raw_smp_processor_id() != pool->cpu);
 
         /* claim and dequeue */
         debug_work_deactivate(work);
         hash_add(pool->busy_hash, &worker->hentry, (unsigned long)work);
         worker->current_work = work;
         worker->current_func = work->func;
         worker->current_pwq = pwq;
         if (worker->task)
                 worker->current_at = worker->task->se.sum_exec_runtime;
         work_data = *work_data_bits(work);
         worker->current_color = get_work_color(work_data);
 
         /*
          * Record wq name for cmdline and debug reporting, may get
          * overridden through set_worker_desc().
          */
         strscpy(worker->desc, pwq->wq->name, WORKER_DESC_LEN);
 
         list_del_init(&work->entry);
 
         /*
          * CPU intensive works don't participate in concurrency management.
          * They're the scheduler's responsibility.  This takes @worker out
          * of concurrency management and the next code block will chain
          * execution of the pending work items.
          */
         if (unlikely(pwq->wq->flags & WQ_CPU_INTENSIVE))
                 worker_set_flags(worker, WORKER_CPU_INTENSIVE);
 
         /*
          * Kick @pool if necessary. It's always noop for per-cpu worker pools
          * since nr_running would always be >= 1 at this point. This is used to
          * chain execution of the pending work items for WORKER_NOT_RUNNING
          * workers such as the UNBOUND and CPU_INTENSIVE ones.
          */
         kick_pool(pool);
 
         /*
          * Record the last pool and clear PENDING which should be the last
          * update to @work.  Also, do this inside @pool->lock so that
          * PENDING and queued state changes happen together while IRQ is
          * disabled.
          */
         set_work_pool_and_clear_pending(work, pool->id, pool_offq_flags(pool));
 
         pwq->stats[PWQ_STAT_STARTED]++;
         raw_spin_unlock_irq(&pool->lock);
 
         rcu_start_depth = rcu_preempt_depth();
         lockdep_start_depth = lockdep_depth(current);
         /* see drain_dead_softirq_workfn() */
         if (!bh_draining)
                 lock_map_acquire(&pwq->wq->lockdep_map);
         lock_map_acquire(&lockdep_map);
         /*
          * Strictly speaking we should mark the invariant state without holding
          * any locks, that is, before these two lock_map_acquire()'s.
          *
          * However, that would result in:
          *
          *   A(W1)
          *   WFC(C)
          *              A(W1)
          *              C(C)
          *
          * Which would create W1->C->W1 dependencies, even though there is no
          * actual deadlock possible. There are two solutions, using a
          * read-recursive acquire on the work(queue) 'locks', but this will then
          * hit the lockdep limitation on recursive locks, or simply discard
          * these locks.
          *
          * AFAICT there is no possible deadlock scenario between the
          * flush_work() and complete() primitives (except for single-threaded
          * workqueues), so hiding them isn't a problem.
          */
         lockdep_invariant_state(true);
         trace_workqueue_execute_start(work);
         worker->current_func(work);
         /*
          * While we must be careful to not use "work" after this, the trace
          * point will only record its address.
          */
         trace_workqueue_execute_end(work, worker->current_func);
         pwq->stats[PWQ_STAT_COMPLETED]++;
         lock_map_release(&lockdep_map);
         if (!bh_draining)
                 lock_map_release(&pwq->wq->lockdep_map);
 
         if (unlikely((worker->task && in_atomic()) ||
                      lockdep_depth(current) != lockdep_start_depth ||
                      rcu_preempt_depth() != rcu_start_depth)) {
                 pr_err("BUG: workqueue leaked atomic, lock or RCU: %s[%d]\n"
                        "     preempt=0x%08x lock=%d->%d RCU=%d->%d workfn=%ps\n",
                        current->comm, task_pid_nr(current), preempt_count(),
                        lockdep_start_depth, lockdep_depth(current),
                        rcu_start_depth, rcu_preempt_depth(),
                        worker->current_func);
                 debug_show_held_locks(current);
                 dump_stack();
         }
 
         /*
          * The following prevents a kworker from hogging CPU on !PREEMPTION
          * kernels, where a requeueing work item waiting for something to
          * happen could deadlock with stop_machine as such work item could
          * indefinitely requeue itself while all other CPUs are trapped in
          * stop_machine. At the same time, report a quiescent RCU state so
          * the same condition doesn't freeze RCU.
          */
         if (worker->task)
                 cond_resched();
 
         raw_spin_lock_irq(&pool->lock);
 
         /*
          * In addition to %WQ_CPU_INTENSIVE, @worker may also have been marked
          * CPU intensive by wq_worker_tick() if @work hogged CPU longer than
          * wq_cpu_intensive_thresh_us. Clear it.
          */
         worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
 
         /* tag the worker for identification in schedule() */
         worker->last_func = worker->current_func;
 
         /* we're done with it, release */
         hash_del(&worker->hentry);
         worker->current_work = NULL;
         worker->current_func = NULL;
         worker->current_pwq = NULL;
         worker->current_color = INT_MAX;
 
         /* must be the last step, see the function comment */
         pwq_dec_nr_in_flight(pwq, work_data);
 }
 
 /**
  * process_scheduled_works - process scheduled works
  * @worker: self
  *
  * Process all scheduled works.  Please note that the scheduled list
  * may change while processing a work, so this function repeatedly
  * fetches a work from the top and executes it.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.
  */
 static void process_scheduled_works(struct worker *worker)
 {
         struct work_struct *work;
         bool first = true;
 
         while ((work = list_first_entry_or_null(&worker->scheduled,
                                                 struct work_struct, entry))) {
                 if (first) {
                         worker->pool->watchdog_ts = jiffies;
                         first = false;
                 }
                 process_one_work(worker, work);
         }
 }
 
 static void set_pf_worker(bool val)
 {
         mutex_lock(&wq_pool_attach_mutex);
         if (val)
                 current->flags |= PF_WQ_WORKER;
         else
                 current->flags &= ~PF_WQ_WORKER;
         mutex_unlock(&wq_pool_attach_mutex);
 }
 
 /**
  * worker_thread - the worker thread function
  * @__worker: self
  *
  * The worker thread function.  All workers belong to a worker_pool -
  * either a per-cpu one or dynamic unbound one.  These workers process all
  * work items regardless of their specific target workqueue.  The only
  * exception is work items which belong to workqueues with a rescuer which
  * will be explained in rescuer_thread().
  *
  * Return: 0
  */
 static int worker_thread(void *__worker)
 {
         struct worker *worker = __worker;
         struct worker_pool *pool = worker->pool;
 
         /* tell the scheduler that this is a workqueue worker */
         set_pf_worker(true);
 woke_up:
         raw_spin_lock_irq(&pool->lock);
 
         /* am I supposed to die? */
         if (unlikely(worker->flags & WORKER_DIE)) {
                 raw_spin_unlock_irq(&pool->lock);
                 set_pf_worker(false);
 
                 ida_free(&pool->worker_ida, worker->id);
                 WARN_ON_ONCE(!list_empty(&worker->entry));
                 return 0;
         }
 
         worker_leave_idle(worker);
 recheck:
         /* no more worker necessary? */
         if (!need_more_worker(pool))
                 goto sleep;
 
         /* do we need to manage? */
         if (unlikely(!may_start_working(pool)) && manage_workers(worker))
                 goto recheck;
 
         /*
          * ->scheduled list can only be filled while a worker is
          * preparing to process a work or actually processing it.
          * Make sure nobody diddled with it while I was sleeping.
          */
         WARN_ON_ONCE(!list_empty(&worker->scheduled));
 
         /*
          * Finish PREP stage.  We're guaranteed to have at least one idle
          * worker or that someone else has already assumed the manager
          * role.  This is where @worker starts participating in concurrency
          * management if applicable and concurrency management is restored
          * after being rebound.  See rebind_workers() for details.
          */
         worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
 
         do {
                 struct work_struct *work =
                         list_first_entry(&pool->worklist,
                                          struct work_struct, entry);
 
                 if (assign_work(work, worker, NULL))
                         process_scheduled_works(worker);
         } while (keep_working(pool));
 
         worker_set_flags(worker, WORKER_PREP);
 sleep:
         /*
          * pool->lock is held and there's no work to process and no need to
          * manage, sleep.  Workers are woken up only while holding
          * pool->lock or from local cpu, so setting the current state
          * before releasing pool->lock is enough to prevent losing any
          * event.
          */
         worker_enter_idle(worker);
         __set_current_state(TASK_IDLE);
         raw_spin_unlock_irq(&pool->lock);
         schedule();
         goto woke_up;
 }
 
 /**
  * rescuer_thread - the rescuer thread function
  * @__rescuer: self
  *
  * Workqueue rescuer thread function.  There's one rescuer for each
  * workqueue which has WQ_MEM_RECLAIM set.
  *
  * Regular work processing on a pool may block trying to create a new
  * worker which uses GFP_KERNEL allocation which has slight chance of
  * developing into deadlock if some works currently on the same queue
  * need to be processed to satisfy the GFP_KERNEL allocation.  This is
  * the problem rescuer solves.
  *
  * When such condition is possible, the pool summons rescuers of all
  * workqueues which have works queued on the pool and let them process
  * those works so that forward progress can be guaranteed.
  *
  * This should happen rarely.
  *
  * Return: 0
  */
 static int rescuer_thread(void *__rescuer)
 {
         struct worker *rescuer = __rescuer;
         struct workqueue_struct *wq = rescuer->rescue_wq;
         bool should_stop;
 
         set_user_nice(current, RESCUER_NICE_LEVEL);
 
         /*
          * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
          * doesn't participate in concurrency management.
          */
         set_pf_worker(true);
 repeat:
         set_current_state(TASK_IDLE);
 
         /*
          * By the time the rescuer is requested to stop, the workqueue
          * shouldn't have any work pending, but @wq->maydays may still have
          * pwq(s) queued.  This can happen by non-rescuer workers consuming
          * all the work items before the rescuer got to them.  Go through
          * @wq->maydays processing before acting on should_stop so that the
          * list is always empty on exit.
          */
         should_stop = kthread_should_stop();
 
         /* see whether any pwq is asking for help */
         raw_spin_lock_irq(&wq_mayday_lock);
 
         while (!list_empty(&wq->maydays)) {
                 struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
                                         struct pool_workqueue, mayday_node);
                 struct worker_pool *pool = pwq->pool;
                 struct work_struct *work, *n;
 
                 __set_current_state(TASK_RUNNING);
                 list_del_init(&pwq->mayday_node);
 
                 raw_spin_unlock_irq(&wq_mayday_lock);
 
                 worker_attach_to_pool(rescuer, pool);
 
                 raw_spin_lock_irq(&pool->lock);
 
                 /*
                  * Slurp in all works issued via this workqueue and
                  * process'em.
                  */
                 WARN_ON_ONCE(!list_empty(&rescuer->scheduled));
                 list_for_each_entry_safe(work, n, &pool->worklist, entry) {
                         if (get_work_pwq(work) == pwq &&
                             assign_work(work, rescuer, &n))
                                 pwq->stats[PWQ_STAT_RESCUED]++;
                 }
 
                 if (!list_empty(&rescuer->scheduled)) {
                         process_scheduled_works(rescuer);
 
                         /*
                          * The above execution of rescued work items could
                          * have created more to rescue through
                          * pwq_activate_first_inactive() or chained
                          * queueing.  Let's put @pwq back on mayday list so
                          * that such back-to-back work items, which may be
                          * being used to relieve memory pressure, don't
                          * incur MAYDAY_INTERVAL delay inbetween.
                          */
                         if (pwq->nr_active && need_to_create_worker(pool)) {
                                 raw_spin_lock(&wq_mayday_lock);
                                 /*
                                  * Queue iff we aren't racing destruction
                                  * and somebody else hasn't queued it already.
                                  */
                                 if (wq->rescuer && list_empty(&pwq->mayday_node)) {
                                         get_pwq(pwq);
                                         list_add_tail(&pwq->mayday_node, &wq->maydays);
                                 }
                                 raw_spin_unlock(&wq_mayday_lock);
                         }
                 }
 
                 /*
                  * Put the reference grabbed by send_mayday().  @pool won't
                  * go away while we're still attached to it.
                  */
                 put_pwq(pwq);
 
                 /*
                  * Leave this pool. Notify regular workers; otherwise, we end up
                  * with 0 concurrency and stalling the execution.
                  */
                 kick_pool(pool);
 
                 raw_spin_unlock_irq(&pool->lock);
 
                 worker_detach_from_pool(rescuer);
 
                 raw_spin_lock_irq(&wq_mayday_lock);
         }
 
         raw_spin_unlock_irq(&wq_mayday_lock);
 
         if (should_stop) {
                 __set_current_state(TASK_RUNNING);
                 set_pf_worker(false);
                 return 0;
         }
 
         /* rescuers should never participate in concurrency management */
         WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
         schedule();
         goto repeat;
 }
 
 static void bh_worker(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
         int nr_restarts = BH_WORKER_RESTARTS;
         unsigned long end = jiffies + BH_WORKER_JIFFIES;
 
         raw_spin_lock_irq(&pool->lock);
         worker_leave_idle(worker);
 
         /*
          * This function follows the structure of worker_thread(). See there for
          * explanations on each step.
          */
         if (!need_more_worker(pool))
                 goto done;
 
         WARN_ON_ONCE(!list_empty(&worker->scheduled));
         worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
 
         do {
                 struct work_struct *work =
                         list_first_entry(&pool->worklist,
                                          struct work_struct, entry);
 
                 if (assign_work(work, worker, NULL))
                         process_scheduled_works(worker);
         } while (keep_working(pool) &&
                  --nr_restarts && time_before(jiffies, end));
 
         worker_set_flags(worker, WORKER_PREP);
 done:
         worker_enter_idle(worker);
         kick_pool(pool);
         raw_spin_unlock_irq(&pool->lock);
 }
 
 /*
  * TODO: Convert all tasklet users to workqueue and use softirq directly.
  *
  * This is currently called from tasklet[_hi]action() and thus is also called
  * whenever there are tasklets to run. Let's do an early exit if there's nothing
  * queued. Once conversion from tasklet is complete, the need_more_worker() test
  * can be dropped.
  *
  * After full conversion, we'll add worker->softirq_action, directly use the
  * softirq action and obtain the worker pointer from the softirq_action pointer.
  */
 void workqueue_softirq_action(bool highpri)
 {
         struct worker_pool *pool =
                 &per_cpu(bh_worker_pools, smp_processor_id())[highpri];
         if (need_more_worker(pool))
                 bh_worker(list_first_entry(&pool->workers, struct worker, node));
 }
 
 struct wq_drain_dead_softirq_work {
         struct work_struct      work;
         struct worker_pool      *pool;
         struct completion       done;
 };
 
 static void drain_dead_softirq_workfn(struct work_struct *work)
 {
         struct wq_drain_dead_softirq_work *dead_work =
                 container_of(work, struct wq_drain_dead_softirq_work, work);
         struct worker_pool *pool = dead_work->pool;
         bool repeat;
 
         /*
          * @pool's CPU is dead and we want to execute its still pending work
          * items from this BH work item which is running on a different CPU. As
          * its CPU is dead, @pool can't be kicked and, as work execution path
          * will be nested, a lockdep annotation needs to be suppressed. Mark
          * @pool with %POOL_BH_DRAINING for the special treatments.
          */
         raw_spin_lock_irq(&pool->lock);
         pool->flags |= POOL_BH_DRAINING;
         raw_spin_unlock_irq(&pool->lock);
 
         bh_worker(list_first_entry(&pool->workers, struct worker, node));
 
         raw_spin_lock_irq(&pool->lock);
         pool->flags &= ~POOL_BH_DRAINING;
         repeat = need_more_worker(pool);
         raw_spin_unlock_irq(&pool->lock);
 
         /*
          * bh_worker() might hit consecutive execution limit and bail. If there
          * still are pending work items, reschedule self and return so that we
          * don't hog this CPU's BH.
          */
         if (repeat) {
                 if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
                         queue_work(system_bh_highpri_wq, work);
                 else
                         queue_work(system_bh_wq, work);
         } else {
                 complete(&dead_work->done);
         }
 }
 
 /*
  * @cpu is dead. Drain the remaining BH work items on the current CPU. It's
  * possible to allocate dead_work per CPU and avoid flushing. However, then we
  * have to worry about draining overlapping with CPU coming back online or
  * nesting (one CPU's dead_work queued on another CPU which is also dead and so
  * on). Let's keep it simple and drain them synchronously. These are BH work
  * items which shouldn't be requeued on the same pool. Shouldn't take long.
  */
 void workqueue_softirq_dead(unsigned int cpu)
 {
         int i;
 
         for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
                 struct worker_pool *pool = &per_cpu(bh_worker_pools, cpu)[i];
                 struct wq_drain_dead_softirq_work dead_work;
 
                 if (!need_more_worker(pool))
                         continue;
 
                 INIT_WORK_ONSTACK(&dead_work.work, drain_dead_softirq_workfn);
                 dead_work.pool = pool;
                 init_completion(&dead_work.done);
 
                 if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
                         queue_work(system_bh_highpri_wq, &dead_work.work);
                 else
                         queue_work(system_bh_wq, &dead_work.work);
 
                 wait_for_completion(&dead_work.done);
                 destroy_work_on_stack(&dead_work.work);
         }
 }
 
 /**
  * check_flush_dependency - check for flush dependency sanity
  * @target_wq: workqueue being flushed
  * @target_work: work item being flushed (NULL for workqueue flushes)
  *
  * %current is trying to flush the whole @target_wq or @target_work on it.
  * If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not
  * reclaiming memory or running on a workqueue which doesn't have
  * %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to
  * a deadlock.
  */
 static void check_flush_dependency(struct workqueue_struct *target_wq,
                                    struct work_struct *target_work)
 {
         work_func_t target_func = target_work ? target_work->func : NULL;
         struct worker *worker;
 
         if (target_wq->flags & WQ_MEM_RECLAIM)
                 return;
 
         worker = current_wq_worker();
 
         WARN_ONCE(current->flags & PF_MEMALLOC,
                   "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%ps",
                   current->pid, current->comm, target_wq->name, target_func);
         WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
                               (WQ_MEM_RECLAIM | __WQ_LEGACY)) == WQ_MEM_RECLAIM),
                   "workqueue: WQ_MEM_RECLAIM %s:%ps is flushing !WQ_MEM_RECLAIM %s:%ps",
                   worker->current_pwq->wq->name, worker->current_func,
                   target_wq->name, target_func);
 }
 
 struct wq_barrier {
         struct work_struct      work;
         struct completion       done;
         struct task_struct      *task;  /* purely informational */
 };
 
 static void wq_barrier_func(struct work_struct *work)
 {
         struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
         complete(&barr->done);
 }
 
 /**
  * insert_wq_barrier - insert a barrier work
  * @pwq: pwq to insert barrier into
  * @barr: wq_barrier to insert
  * @target: target work to attach @barr to
  * @worker: worker currently executing @target, NULL if @target is not executing
  *
  * @barr is linked to @target such that @barr is completed only after
  * @target finishes execution.  Please note that the ordering
  * guarantee is observed only with respect to @target and on the local
  * cpu.
  *
  * Currently, a queued barrier can't be canceled.  This is because
  * try_to_grab_pending() can't determine whether the work to be
  * grabbed is at the head of the queue and thus can't clear LINKED
  * flag of the previous work while there must be a valid next work
  * after a work with LINKED flag set.
  *
  * Note that when @worker is non-NULL, @target may be modified
  * underneath us, so we can't reliably determine pwq from @target.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
 static void insert_wq_barrier(struct pool_workqueue *pwq,
                               struct wq_barrier *barr,
                               struct work_struct *target, struct worker *worker)
 {
         static __maybe_unused struct lock_class_key bh_key, thr_key;
         unsigned int work_flags = 0;
         unsigned int work_color;
         struct list_head *head;
 
         /*
          * debugobject calls are safe here even with pool->lock locked
          * as we know for sure that this will not trigger any of the
          * checks and call back into the fixup functions where we
          * might deadlock.
          *
          * BH and threaded workqueues need separate lockdep keys to avoid
          * spuriously triggering "inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W}
          * usage".
          */
         INIT_WORK_ONSTACK_KEY(&barr->work, wq_barrier_func,
                               (pwq->wq->flags & WQ_BH) ? &bh_key : &thr_key);
         __set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
 
         init_completion_map(&barr->done, &target->lockdep_map);
 
         barr->task = current;
 
         /* The barrier work item does not participate in nr_active. */
         work_flags |= WORK_STRUCT_INACTIVE;
 
         /*
          * If @target is currently being executed, schedule the
          * barrier to the worker; otherwise, put it after @target.
          */
         if (worker) {
                 head = worker->scheduled.next;
                 work_color = worker->current_color;
         } else {
                 unsigned long *bits = work_data_bits(target);
 
                 head = target->entry.next;
                 /* there can already be other linked works, inherit and set */
                 work_flags |= *bits & WORK_STRUCT_LINKED;
                 work_color = get_work_color(*bits);
                 __set_bit(WORK_STRUCT_LINKED_BIT, bits);
         }
 
         pwq->nr_in_flight[work_color]++;
         work_flags |= work_color_to_flags(work_color);
 
         insert_work(pwq, &barr->work, head, work_flags);
 }
 
 /**
  * flush_workqueue_prep_pwqs - prepare pwqs for workqueue flushing
  * @wq: workqueue being flushed
  * @flush_color: new flush color, < 0 for no-op
  * @work_color: new work color, < 0 for no-op
  *
  * Prepare pwqs for workqueue flushing.
  *
  * If @flush_color is non-negative, flush_color on all pwqs should be
  * -1.  If no pwq has in-flight commands at the specified color, all
  * pwq->flush_color's stay at -1 and %false is returned.  If any pwq
  * has in flight commands, its pwq->flush_color is set to
  * @flush_color, @wq->nr_pwqs_to_flush is updated accordingly, pwq
  * wakeup logic is armed and %true is returned.
  *
  * The caller should have initialized @wq->first_flusher prior to
  * calling this function with non-negative @flush_color.  If
  * @flush_color is negative, no flush color update is done and %false
  * is returned.
  *
  * If @work_color is non-negative, all pwqs should have the same
  * work_color which is previous to @work_color and all will be
  * advanced to @work_color.
  *
  * CONTEXT:
  * mutex_lock(wq->mutex).
  *
  * Return:
  * %true if @flush_color >= 0 and there's something to flush.  %false
  * otherwise.
  */
 static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
                                       int flush_color, int work_color)
 {
         bool wait = false;
         struct pool_workqueue *pwq;
 
         if (flush_color >= 0) {
                 WARN_ON_ONCE(atomic_read(&wq->nr_pwqs_to_flush));
                 atomic_set(&wq->nr_pwqs_to_flush, 1);
         }
 
         for_each_pwq(pwq, wq) {
                 struct worker_pool *pool = pwq->pool;
 
                 raw_spin_lock_irq(&pool->lock);
 
                 if (flush_color >= 0) {
                         WARN_ON_ONCE(pwq->flush_color != -1);
 
                         if (pwq->nr_in_flight[flush_color]) {
                                 pwq->flush_color = flush_color;
                                 atomic_inc(&wq->nr_pwqs_to_flush);
                                 wait = true;
                         }
                 }
 
                 if (work_color >= 0) {
                         WARN_ON_ONCE(work_color != work_next_color(pwq->work_color));
                         pwq->work_color = work_color;
                 }
 
                 raw_spin_unlock_irq(&pool->lock);
         }
 
         if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
                 complete(&wq->first_flusher->done);
 
         return wait;
 }
 
 static void touch_wq_lockdep_map(struct workqueue_struct *wq)
 {
 #ifdef CONFIG_LOCKDEP
         if (wq->flags & WQ_BH)
                 local_bh_disable();
 
         lock_map_acquire(&wq->lockdep_map);
         lock_map_release(&wq->lockdep_map);
 
         if (wq->flags & WQ_BH)
                 local_bh_enable();
 #endif
 }
 
 static void touch_work_lockdep_map(struct work_struct *work,
                                    struct workqueue_struct *wq)
 {
 #ifdef CONFIG_LOCKDEP
         if (wq->flags & WQ_BH)
                 local_bh_disable();
 
         lock_map_acquire(&work->lockdep_map);
         lock_map_release(&work->lockdep_map);
 
         if (wq->flags & WQ_BH)
                 local_bh_enable();
 #endif
 }
 
 /**
  * __flush_workqueue - ensure that any scheduled work has run to completion.
  * @wq: workqueue to flush
  *
  * This function sleeps until all work items which were queued on entry
  * have finished execution, but it is not livelocked by new incoming ones.
  */
 void __flush_workqueue(struct workqueue_struct *wq)
 {
         struct wq_flusher this_flusher = {
                 .list = LIST_HEAD_INIT(this_flusher.list),
                 .flush_color = -1,
                 .done = COMPLETION_INITIALIZER_ONSTACK_MAP(this_flusher.done, wq->lockdep_map),
         };
         int next_color;
 
         if (WARN_ON(!wq_online))
                 return;
 
         touch_wq_lockdep_map(wq);
 
         mutex_lock(&wq->mutex);
 
         /*
          * Start-to-wait phase
          */
         next_color = work_next_color(wq->work_color);
 
         if (next_color != wq->flush_color) {
                 /*
                  * Color space is not full.  The current work_color
                  * becomes our flush_color and work_color is advanced
                  * by one.
                  */
                 WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
                 this_flusher.flush_color = wq->work_color;
                 wq->work_color = next_color;
 
                 if (!wq->first_flusher) {
                         /* no flush in progress, become the first flusher */
                         WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
 
                         wq->first_flusher = &this_flusher;
 
                         if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
                                                        wq->work_color)) {
                                 /* nothing to flush, done */
                                 wq->flush_color = next_color;
                                 wq->first_flusher = NULL;
                                 goto out_unlock;
                         }
                 } else {
                         /* wait in queue */
                         WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
                         list_add_tail(&this_flusher.list, &wq->flusher_queue);
                         flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
                 }
         } else {
                 /*
                  * Oops, color space is full, wait on overflow queue.
                  * The next flush completion will assign us
                  * flush_color and transfer to flusher_queue.
                  */
                 list_add_tail(&this_flusher.list, &wq->flusher_overflow);
         }
 
         check_flush_dependency(wq, NULL);
 
         mutex_unlock(&wq->mutex);
 
         wait_for_completion(&this_flusher.done);
 
         /*
          * Wake-up-and-cascade phase
          *
          * First flushers are responsible for cascading flushes and
          * handling overflow.  Non-first flushers can simply return.
          */
         if (READ_ONCE(wq->first_flusher) != &this_flusher)
                 return;
 
         mutex_lock(&wq->mutex);
 
         /* we might have raced, check again with mutex held */
         if (wq->first_flusher != &this_flusher)
                 goto out_unlock;
 
         WRITE_ONCE(wq->first_flusher, NULL);
 
         WARN_ON_ONCE(!list_empty(&this_flusher.list));
         WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
 
         while (true) {
                 struct wq_flusher *next, *tmp;
 
                 /* complete all the flushers sharing the current flush color */
                 list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
                         if (next->flush_color != wq->flush_color)
                                 break;
                         list_del_init(&next->list);
                         complete(&next->done);
                 }
 
                 WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
                              wq->flush_color != work_next_color(wq->work_color));
 
                 /* this flush_color is finished, advance by one */
                 wq->flush_color = work_next_color(wq->flush_color);
 
                 /* one color has been freed, handle overflow queue */
                 if (!list_empty(&wq->flusher_overflow)) {
                         /*
                          * Assign the same color to all overflowed
                          * flushers, advance work_color and append to
                          * flusher_queue.  This is the start-to-wait
                          * phase for these overflowed flushers.
                          */
                         list_for_each_entry(tmp, &wq->flusher_overflow, list)
                                 tmp->flush_color = wq->work_color;
 
                         wq->work_color = work_next_color(wq->work_color);
 
                         list_splice_tail_init(&wq->flusher_overflow,
                                               &wq->flusher_queue);
                         flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
                 }
 
                 if (list_empty(&wq->flusher_queue)) {
                         WARN_ON_ONCE(wq->flush_color != wq->work_color);
                         break;
                 }
 
                 /*
                  * Need to flush more colors.  Make the next flusher
                  * the new first flusher and arm pwqs.
                  */
                 WARN_ON_ONCE(wq->flush_color == wq->work_color);
                 WARN_ON_ONCE(wq->flush_color != next->flush_color);
 
                 list_del_init(&next->list);
                 wq->first_flusher = next;
 
                 if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
                         break;
 
                 /*
                  * Meh... this color is already done, clear first
                  * flusher and repeat cascading.
                  */
                 wq->first_flusher = NULL;
         }
 
 out_unlock:
         mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL(__flush_workqueue);
 
 /**
  * drain_workqueue - drain a workqueue
  * @wq: workqueue to drain
  *
  * Wait until the workqueue becomes empty.  While draining is in progress,
  * only chain queueing is allowed.  IOW, only currently pending or running
  * work items on @wq can queue further work items on it.  @wq is flushed
  * repeatedly until it becomes empty.  The number of flushing is determined
  * by the depth of chaining and should be relatively short.  Whine if it
  * takes too long.
  */
 void drain_workqueue(struct workqueue_struct *wq)
 {
         unsigned int flush_cnt = 0;
         struct pool_workqueue *pwq;
 
         /*
          * __queue_work() needs to test whether there are drainers, is much
          * hotter than drain_workqueue() and already looks at @wq->flags.
          * Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
          */
         mutex_lock(&wq->mutex);
         if (!wq->nr_drainers++)
                 wq->flags |= __WQ_DRAINING;
         mutex_unlock(&wq->mutex);
 reflush:
         __flush_workqueue(wq);
 
         mutex_lock(&wq->mutex);
 
         for_each_pwq(pwq, wq) {
                 bool drained;
 
                 raw_spin_lock_irq(&pwq->pool->lock);
                 drained = pwq_is_empty(pwq);
                 raw_spin_unlock_irq(&pwq->pool->lock);
 
                 if (drained)
                         continue;
 
                 if (++flush_cnt == 10 ||
                     (flush_cnt % 100 == 0 && flush_cnt <= 1000))
                         pr_warn("workqueue %s: %s() isn't complete after %u tries\n",
                                 wq->name, __func__, flush_cnt);
 
                 mutex_unlock(&wq->mutex);
                 goto reflush;
         }
 
         if (!--wq->nr_drainers)
                 wq->flags &= ~__WQ_DRAINING;
         mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL_GPL(drain_workqueue);
 
 static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
                              bool from_cancel)
 {
         struct worker *worker = NULL;
         struct worker_pool *pool;
         struct pool_workqueue *pwq;
         struct workqueue_struct *wq;
 
         rcu_read_lock();
         pool = get_work_pool(work);
         if (!pool) {
                 rcu_read_unlock();
                 return false;
         }
 
         raw_spin_lock_irq(&pool->lock);
         /* see the comment in try_to_grab_pending() with the same code */
         pwq = get_work_pwq(work);
         if (pwq) {
                 if (unlikely(pwq->pool != pool))
                         goto already_gone;
         } else {
                 worker = find_worker_executing_work(pool, work);
                 if (!worker)
                         goto already_gone;
                 pwq = worker->current_pwq;
         }
 
         wq = pwq->wq;
         check_flush_dependency(wq, work);
 
         insert_wq_barrier(pwq, barr, work, worker);
         raw_spin_unlock_irq(&pool->lock);
 
         touch_work_lockdep_map(work, wq);
 
         /*
          * Force a lock recursion deadlock when using flush_work() inside a
          * single-threaded or rescuer equipped workqueue.
          *
          * For single threaded workqueues the deadlock happens when the work
          * is after the work issuing the flush_work(). For rescuer equipped
          * workqueues the deadlock happens when the rescuer stalls, blocking
          * forward progress.
          */
         if (!from_cancel && (wq->saved_max_active == 1 || wq->rescuer))
                 touch_wq_lockdep_map(wq);
 
         rcu_read_unlock();
         return true;
 already_gone:
         raw_spin_unlock_irq(&pool->lock);
         rcu_read_unlock();
         return false;
 }
 
 static bool __flush_work(struct work_struct *work, bool from_cancel)
 {
         struct wq_barrier barr;
         unsigned long data;
 
         if (WARN_ON(!wq_online))
                 return false;
 
         if (WARN_ON(!work->func))
                 return false;
 
         if (!start_flush_work(work, &barr, from_cancel))
                 return false;
 
         /*
          * start_flush_work() returned %true. If @from_cancel is set, we know
          * that @work must have been executing during start_flush_work() and
          * can't currently be queued. Its data must contain OFFQ bits. If @work
          * was queued on a BH workqueue, we also know that it was running in the
          * BH context and thus can be busy-waited.
          */
         data = *work_data_bits(work);
         if (from_cancel &&
             !WARN_ON_ONCE(data & WORK_STRUCT_PWQ) && (data & WORK_OFFQ_BH)) {
                 /*
                  * On RT, prevent a live lock when %current preempted soft
                  * interrupt processing or prevents ksoftirqd from running by
                  * keeping flipping BH. If the BH work item runs on a different
                  * CPU then this has no effect other than doing the BH
                  * disable/enable dance for nothing. This is copied from
                  * kernel/softirq.c::tasklet_unlock_spin_wait().
                  */
                 while (!try_wait_for_completion(&barr.done)) {
                         if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
                                 local_bh_disable();
                                 local_bh_enable();
                         } else {
                                 cpu_relax();
                         }
                 }
         } else {
                 wait_for_completion(&barr.done);
         }
 
         destroy_work_on_stack(&barr.work);
         return true;
 }
 
 /**
  * flush_work - wait for a work to finish executing the last queueing instance
  * @work: the work to flush
  *
  * Wait until @work has finished execution.  @work is guaranteed to be idle
  * on return if it hasn't been requeued since flush started.
  *
  * Return:
  * %true if flush_work() waited for the work to finish execution,
  * %false if it was already idle.
  */
 bool flush_work(struct work_struct *work)
 {
         might_sleep();
         return __flush_work(work, false);
 }
 EXPORT_SYMBOL_GPL(flush_work);
 
 /**
  * flush_delayed_work - wait for a dwork to finish executing the last queueing
  * @dwork: the delayed work to flush
  *
  * Delayed timer is cancelled and the pending work is queued for
  * immediate execution.  Like flush_work(), this function only
  * considers the last queueing instance of @dwork.
  *
  * Return:
  * %true if flush_work() waited for the work to finish execution,
  * %false if it was already idle.
  */
 bool flush_delayed_work(struct delayed_work *dwork)
 {
         local_irq_disable();
         if (del_timer_sync(&dwork->timer))
                 __queue_work(dwork->cpu, dwork->wq, &dwork->work);
         local_irq_enable();
         return flush_work(&dwork->work);
 }
 EXPORT_SYMBOL(flush_delayed_work);
 
 /**
  * flush_rcu_work - wait for a rwork to finish executing the last queueing
  * @rwork: the rcu work to flush
  *
  * Return:
  * %true if flush_rcu_work() waited for the work to finish execution,
  * %false if it was already idle.
  */
 bool flush_rcu_work(struct rcu_work *rwork)
 {
         if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
                 rcu_barrier();
                 flush_work(&rwork->work);
                 return true;
         } else {
                 return flush_work(&rwork->work);
         }
 }
 EXPORT_SYMBOL(flush_rcu_work);
 
 static void work_offqd_disable(struct work_offq_data *offqd)
 {
         const unsigned long max = (1lu << WORK_OFFQ_DISABLE_BITS) - 1;
 
         if (likely(offqd->disable < max))
                 offqd->disable++;
         else
                 WARN_ONCE(true, "workqueue: work disable count overflowed\n");
 }
 
 static void work_offqd_enable(struct work_offq_data *offqd)
 {
         if (likely(offqd->disable > 0))
                 offqd->disable--;
         else
                 WARN_ONCE(true, "workqueue: work disable count underflowed\n");
 }
 
 static bool __cancel_work(struct work_struct *work, u32 cflags)
 {
         struct work_offq_data offqd;
         unsigned long irq_flags;
         int ret;
 
         ret = work_grab_pending(work, cflags, &irq_flags);
 
         work_offqd_unpack(&offqd, *work_data_bits(work));
 
         if (cflags & WORK_CANCEL_DISABLE)
                 work_offqd_disable(&offqd);
 
         set_work_pool_and_clear_pending(work, offqd.pool_id,
                                         work_offqd_pack_flags(&offqd));
         local_irq_restore(irq_flags);
         return ret;
 }
 
 static bool __cancel_work_sync(struct work_struct *work, u32 cflags)
 {
         bool ret;
 
         ret = __cancel_work(work, cflags | WORK_CANCEL_DISABLE);
 
         if (*work_data_bits(work) & WORK_OFFQ_BH)
                 WARN_ON_ONCE(in_hardirq());
         else
                 might_sleep();
 
         /*
          * Skip __flush_work() during early boot when we know that @work isn't
          * executing. This allows canceling during early boot.
          */
         if (wq_online)
                 __flush_work(work, true);
 
         if (!(cflags & WORK_CANCEL_DISABLE))
                 enable_work(work);
 
         return ret;
 }
 
 /*
  * See cancel_delayed_work()
  */
 bool cancel_work(struct work_struct *work)
 {
         return __cancel_work(work, 0);
 }
 EXPORT_SYMBOL(cancel_work);
 
 /**
  * cancel_work_sync - cancel a work and wait for it to finish
  * @work: the work to cancel
  *
  * Cancel @work and wait for its execution to finish. This function can be used
  * even if the work re-queues itself or migrates to another workqueue. On return
  * from this function, @work is guaranteed to be not pending or executing on any
  * CPU as long as there aren't racing enqueues.
  *
  * cancel_work_sync(&delayed_work->work) must not be used for delayed_work's.
  * Use cancel_delayed_work_sync() instead.
  *
  * Must be called from a sleepable context if @work was last queued on a non-BH
  * workqueue. Can also be called from non-hardirq atomic contexts including BH
  * if @work was last queued on a BH workqueue.
  *
  * Returns %true if @work was pending, %false otherwise.
  */
 bool cancel_work_sync(struct work_struct *work)
 {
         return __cancel_work_sync(work, 0);
 }
 EXPORT_SYMBOL_GPL(cancel_work_sync);
 
 /**
  * cancel_delayed_work - cancel a delayed work
  * @dwork: delayed_work to cancel
  *
  * Kill off a pending delayed_work.
  *
  * Return: %true if @dwork was pending and canceled; %false if it wasn't
  * pending.
  *
  * Note:
  * The work callback function may still be running on return, unless
  * it returns %true and the work doesn't re-arm itself.  Explicitly flush or
  * use cancel_delayed_work_sync() to wait on it.
  *
  * This function is safe to call from any context including IRQ handler.
  */
 bool cancel_delayed_work(struct delayed_work *dwork)
 {
         return __cancel_work(&dwork->work, WORK_CANCEL_DELAYED);
 }
 EXPORT_SYMBOL(cancel_delayed_work);
 
 /**
  * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
  * @dwork: the delayed work cancel
  *
  * This is cancel_work_sync() for delayed works.
  *
  * Return:
  * %true if @dwork was pending, %false otherwise.
  */
 bool cancel_delayed_work_sync(struct delayed_work *dwork)
 {
         return __cancel_work_sync(&dwork->work, WORK_CANCEL_DELAYED);
 }
 EXPORT_SYMBOL(cancel_delayed_work_sync);
 
 /**
  * disable_work - Disable and cancel a work item
  * @work: work item to disable
  *
  * Disable @work by incrementing its disable count and cancel it if currently
  * pending. As long as the disable count is non-zero, any attempt to queue @work
  * will fail and return %false. The maximum supported disable depth is 2 to the
  * power of %WORK_OFFQ_DISABLE_BITS, currently 65536.
  *
  * Can be called from any context. Returns %true if @work was pending, %false
  * otherwise.
  */
 bool disable_work(struct work_struct *work)
 {
         return __cancel_work(work, WORK_CANCEL_DISABLE);
 }
 EXPORT_SYMBOL_GPL(disable_work);
 
 /**
  * disable_work_sync - Disable, cancel and drain a work item
  * @work: work item to disable
  *
  * Similar to disable_work() but also wait for @work to finish if currently
  * executing.
  *
  * Must be called from a sleepable context if @work was last queued on a non-BH
  * workqueue. Can also be called from non-hardirq atomic contexts including BH
  * if @work was last queued on a BH workqueue.
  *
  * Returns %true if @work was pending, %false otherwise.
  */
 bool disable_work_sync(struct work_struct *work)
 {
         return __cancel_work_sync(work, WORK_CANCEL_DISABLE);
 }
 EXPORT_SYMBOL_GPL(disable_work_sync);
 
 /**
  * enable_work - Enable a work item
  * @work: work item to enable
  *
  * Undo disable_work[_sync]() by decrementing @work's disable count. @work can
  * only be queued if its disable count is 0.
  *
  * Can be called from any context. Returns %true if the disable count reached 0.
  * Otherwise, %false.
  */
 bool enable_work(struct work_struct *work)
 {
         struct work_offq_data offqd;
         unsigned long irq_flags;
 
         work_grab_pending(work, 0, &irq_flags);
 
         work_offqd_unpack(&offqd, *work_data_bits(work));
         work_offqd_enable(&offqd);
         set_work_pool_and_clear_pending(work, offqd.pool_id,
                                         work_offqd_pack_flags(&offqd));
         local_irq_restore(irq_flags);
 
         return !offqd.disable;
 }
 EXPORT_SYMBOL_GPL(enable_work);
 
 /**
  * disable_delayed_work - Disable and cancel a delayed work item
  * @dwork: delayed work item to disable
  *
  * disable_work() for delayed work items.
  */
 bool disable_delayed_work(struct delayed_work *dwork)
 {
         return __cancel_work(&dwork->work,
                              WORK_CANCEL_DELAYED | WORK_CANCEL_DISABLE);
 }
 EXPORT_SYMBOL_GPL(disable_delayed_work);
 
 /**
  * disable_delayed_work_sync - Disable, cancel and drain a delayed work item
  * @dwork: delayed work item to disable
  *
  * disable_work_sync() for delayed work items.
  */
 bool disable_delayed_work_sync(struct delayed_work *dwork)
 {
         return __cancel_work_sync(&dwork->work,
                                   WORK_CANCEL_DELAYED | WORK_CANCEL_DISABLE);
 }
 EXPORT_SYMBOL_GPL(disable_delayed_work_sync);
 
 /**
  * enable_delayed_work - Enable a delayed work item
  * @dwork: delayed work item to enable
  *
  * enable_work() for delayed work items.
  */
 bool enable_delayed_work(struct delayed_work *dwork)
 {
         return enable_work(&dwork->work);
 }
 EXPORT_SYMBOL_GPL(enable_delayed_work);
 
 /**
  * schedule_on_each_cpu - execute a function synchronously on each online CPU
  * @func: the function to call
  *
  * schedule_on_each_cpu() executes @func on each online CPU using the
  * system workqueue and blocks until all CPUs have completed.
  * schedule_on_each_cpu() is very slow.
  *
  * Return:
  * 0 on success, -errno on failure.
  */
 int schedule_on_each_cpu(work_func_t func)
 {
         int cpu;
         struct work_struct __percpu *works;
 
         works = alloc_percpu(struct work_struct);
         if (!works)
                 return -ENOMEM;
 
         cpus_read_lock();
 
         for_each_online_cpu(cpu) {
                 struct work_struct *work = per_cpu_ptr(works, cpu);
 
                 INIT_WORK(work, func);
                 schedule_work_on(cpu, work);
         }
 
         for_each_online_cpu(cpu)
                 flush_work(per_cpu_ptr(works, cpu));
 
         cpus_read_unlock();
         free_percpu(works);
         return 0;
 }
 
 /**
  * execute_in_process_context - reliably execute the routine with user context
  * @fn:         the function to execute
  * @ew:         guaranteed storage for the execute work structure (must
  *              be available when the work executes)
  *
  * Executes the function immediately if process context is available,
  * otherwise schedules the function for delayed execution.
  *
  * Return:      0 - function was executed
  *              1 - function was scheduled for execution
  */
 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 {
         if (!in_interrupt()) {
                 fn(&ew->work);
                 return 0;
         }
 
         INIT_WORK(&ew->work, fn);
         schedule_work(&ew->work);
 
         return 1;
 }
 EXPORT_SYMBOL_GPL(execute_in_process_context);
 
 /**
  * free_workqueue_attrs - free a workqueue_attrs
  * @attrs: workqueue_attrs to free
  *
  * Undo alloc_workqueue_attrs().
  */
 void free_workqueue_attrs(struct workqueue_attrs *attrs)
 {
         if (attrs) {
                 free_cpumask_var(attrs->cpumask);
                 free_cpumask_var(attrs->__pod_cpumask);
                 kfree(attrs);
         }
 }
 
 /**
  * alloc_workqueue_attrs - allocate a workqueue_attrs
  *
  * Allocate a new workqueue_attrs, initialize with default settings and
  * return it.
  *
  * Return: The allocated new workqueue_attr on success. %NULL on failure.
  */
 struct workqueue_attrs *alloc_workqueue_attrs(void)
 {
         struct workqueue_attrs *attrs;
 
         attrs = kzalloc(sizeof(*attrs), GFP_KERNEL);
         if (!attrs)
                 goto fail;
         if (!alloc_cpumask_var(&attrs->cpumask, GFP_KERNEL))
                 goto fail;
         if (!alloc_cpumask_var(&attrs->__pod_cpumask, GFP_KERNEL))
                 goto fail;
 
         cpumask_copy(attrs->cpumask, cpu_possible_mask);
         attrs->affn_scope = WQ_AFFN_DFL;
         return attrs;
 fail:
         free_workqueue_attrs(attrs);
         return NULL;
 }
 
 static void copy_workqueue_attrs(struct workqueue_attrs *to,
                                  const struct workqueue_attrs *from)
 {
         to->nice = from->nice;
         cpumask_copy(to->cpumask, from->cpumask);
         cpumask_copy(to->__pod_cpumask, from->__pod_cpumask);
         to->affn_strict = from->affn_strict;
 
         /*
          * Unlike hash and equality test, copying shouldn't ignore wq-only
          * fields as copying is used for both pool and wq attrs. Instead,
          * get_unbound_pool() explicitly clears the fields.
          */
         to->affn_scope = from->affn_scope;
         to->ordered = from->ordered;
 }
 
 /*
  * Some attrs fields are workqueue-only. Clear them for worker_pool's. See the
  * comments in 'struct workqueue_attrs' definition.
  */
 static void wqattrs_clear_for_pool(struct workqueue_attrs *attrs)
 {
         attrs->affn_scope = WQ_AFFN_NR_TYPES;
         attrs->ordered = false;
         if (attrs->affn_strict)
                 cpumask_copy(attrs->cpumask, cpu_possible_mask);
 }
 
 /* hash value of the content of @attr */
 static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
 {
         u32 hash = 0;
 
         hash = jhash_1word(attrs->nice, hash);
         hash = jhash_1word(attrs->affn_strict, hash);
         hash = jhash(cpumask_bits(attrs->__pod_cpumask),
                      BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
         if (!attrs->affn_strict)
                 hash = jhash(cpumask_bits(attrs->cpumask),
                              BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
         return hash;
 }
 
 /* content equality test */
 static bool wqattrs_equal(const struct workqueue_attrs *a,
                           const struct workqueue_attrs *b)
 {
         if (a->nice != b->nice)
                 return false;
         if (a->affn_strict != b->affn_strict)
                 return false;
         if (!cpumask_equal(a->__pod_cpumask, b->__pod_cpumask))
                 return false;
         if (!a->affn_strict && !cpumask_equal(a->cpumask, b->cpumask))
                 return false;
         return true;
 }
 
 /* Update @attrs with actually available CPUs */
 static void wqattrs_actualize_cpumask(struct workqueue_attrs *attrs,
                                       const cpumask_t *unbound_cpumask)
 {
         /*
          * Calculate the effective CPU mask of @attrs given @unbound_cpumask. If
          * @attrs->cpumask doesn't overlap with @unbound_cpumask, we fallback to
          * @unbound_cpumask.
          */
         cpumask_and(attrs->cpumask, attrs->cpumask, unbound_cpumask);
         if (unlikely(cpumask_empty(attrs->cpumask)))
                 cpumask_copy(attrs->cpumask, unbound_cpumask);
 }
 
 /* find wq_pod_type to use for @attrs */
 static const struct wq_pod_type *
 wqattrs_pod_type(const struct workqueue_attrs *attrs)
 {
         enum wq_affn_scope scope;
         struct wq_pod_type *pt;
 
         /* to synchronize access to wq_affn_dfl */
         lockdep_assert_held(&wq_pool_mutex);
 
         if (attrs->affn_scope == WQ_AFFN_DFL)
                 scope = wq_affn_dfl;
         else
                 scope = attrs->affn_scope;
 
         pt = &wq_pod_types[scope];
 
         if (!WARN_ON_ONCE(attrs->affn_scope == WQ_AFFN_NR_TYPES) &&
             likely(pt->nr_pods))
                 return pt;
 
         /*
          * Before workqueue_init_topology(), only SYSTEM is available which is
          * initialized in workqueue_init_early().
          */
         pt = &wq_pod_types[WQ_AFFN_SYSTEM];
         BUG_ON(!pt->nr_pods);
         return pt;
 }
 
 /**
  * init_worker_pool - initialize a newly zalloc'd worker_pool
  * @pool: worker_pool to initialize
  *
  * Initialize a newly zalloc'd @pool.  It also allocates @pool->attrs.
  *
  * Return: 0 on success, -errno on failure.  Even on failure, all fields
  * inside @pool proper are initialized and put_unbound_pool() can be called
  * on @pool safely to release it.
  */
 static int init_worker_pool(struct worker_pool *pool)
 {
         raw_spin_lock_init(&pool->lock);
         pool->id = -1;
         pool->cpu = -1;
         pool->node = NUMA_NO_NODE;
         pool->flags |= POOL_DISASSOCIATED;
         pool->watchdog_ts = jiffies;
         INIT_LIST_HEAD(&pool->worklist);
         INIT_LIST_HEAD(&pool->idle_list);
         hash_init(pool->busy_hash);
 
         timer_setup(&pool->idle_timer, idle_worker_timeout, TIMER_DEFERRABLE);
         INIT_WORK(&pool->idle_cull_work, idle_cull_fn);
 
         timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0);
 
         INIT_LIST_HEAD(&pool->workers);
 
         ida_init(&pool->worker_ida);
         INIT_HLIST_NODE(&pool->hash_node);
         pool->refcnt = 1;
 
         /* shouldn't fail above this point */
         pool->attrs = alloc_workqueue_attrs();
         if (!pool->attrs)
                 return -ENOMEM;
 
         wqattrs_clear_for_pool(pool->attrs);
 
         return 0;
 }
 
 #ifdef CONFIG_LOCKDEP
 static void wq_init_lockdep(struct workqueue_struct *wq)
 {
         char *lock_name;
 
         lockdep_register_key(&wq->key);
         lock_name = kasprintf(GFP_KERNEL, "%s%s", "(wq_completion)", wq->name);
         if (!lock_name)
                 lock_name = wq->name;
 
         wq->lock_name = lock_name;
         lockdep_init_map(&wq->lockdep_map, lock_name, &wq->key, 0);
 }
 
 static void wq_unregister_lockdep(struct workqueue_struct *wq)
 {
         lockdep_unregister_key(&wq->key);
 }
 
 static void wq_free_lockdep(struct workqueue_struct *wq)
 {
         if (wq->lock_name != wq->name)
                 kfree(wq->lock_name);
 }
 #else
 static void wq_init_lockdep(struct workqueue_struct *wq)
 {
 }
 
 static void wq_unregister_lockdep(struct workqueue_struct *wq)
 {
 }
 
 static void wq_free_lockdep(struct workqueue_struct *wq)
 {
 }
 #endif
 
 static void free_node_nr_active(struct wq_node_nr_active **nna_ar)
 {
         int node;
 
         for_each_node(node) {
                 kfree(nna_ar[node]);
                 nna_ar[node] = NULL;
         }
 
         kfree(nna_ar[nr_node_ids]);
         nna_ar[nr_node_ids] = NULL;
 }
 
 static void init_node_nr_active(struct wq_node_nr_active *nna)
 {
         nna->max = WQ_DFL_MIN_ACTIVE;
         atomic_set(&nna->nr, 0);
         raw_spin_lock_init(&nna->lock);
         INIT_LIST_HEAD(&nna->pending_pwqs);
 }
 
 /*
  * Each node's nr_active counter will be accessed mostly from its own node and
  * should be allocated in the node.
  */
 static int alloc_node_nr_active(struct wq_node_nr_active **nna_ar)
 {
         struct wq_node_nr_active *nna;
         int node;
 
         for_each_node(node) {
                 nna = kzalloc_node(sizeof(*nna), GFP_KERNEL, node);
                 if (!nna)
                         goto err_free;
                 init_node_nr_active(nna);
                 nna_ar[node] = nna;
         }
 
         /* [nr_node_ids] is used as the fallback */
         nna = kzalloc_node(sizeof(*nna), GFP_KERNEL, NUMA_NO_NODE);
         if (!nna)
                 goto err_free;
         init_node_nr_active(nna);
         nna_ar[nr_node_ids] = nna;
 
         return 0;
 
 err_free:
         free_node_nr_active(nna_ar);
         return -ENOMEM;
 }
 
 static void rcu_free_wq(struct rcu_head *rcu)
 {
         struct workqueue_struct *wq =
                 container_of(rcu, struct workqueue_struct, rcu);
 
         if (wq->flags & WQ_UNBOUND)
                 free_node_nr_active(wq->node_nr_active);
 
         wq_free_lockdep(wq);
         free_percpu(wq->cpu_pwq);
         free_workqueue_attrs(wq->unbound_attrs);
         kfree(wq);
 }
 
 static void rcu_free_pool(struct rcu_head *rcu)
 {
         struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
 
         ida_destroy(&pool->worker_ida);
         free_workqueue_attrs(pool->attrs);
         kfree(pool);
 }
 
 /**
  * put_unbound_pool - put a worker_pool
  * @pool: worker_pool to put
  *
  * Put @pool.  If its refcnt reaches zero, it gets destroyed in RCU
  * safe manner.  get_unbound_pool() calls this function on its failure path
  * and this function should be able to release pools which went through,
  * successfully or not, init_worker_pool().
  *
  * Should be called with wq_pool_mutex held.
  */
 static void put_unbound_pool(struct worker_pool *pool)
 {
         struct worker *worker;
         LIST_HEAD(cull_list);
 
         lockdep_assert_held(&wq_pool_mutex);
 
         if (--pool->refcnt)
                 return;
 
         /* sanity checks */
         if (WARN_ON(!(pool->cpu < 0)) ||
             WARN_ON(!list_empty(&pool->worklist)))
                 return;
 
         /* release id and unhash */
         if (pool->id >= 0)
                 idr_remove(&worker_pool_idr, pool->id);
         hash_del(&pool->hash_node);
 
         /*
          * Become the manager and destroy all workers.  This prevents
          * @pool's workers from blocking on attach_mutex.  We're the last
          * manager and @pool gets freed with the flag set.
          *
          * Having a concurrent manager is quite unlikely to happen as we can
          * only get here with
          *   pwq->refcnt == pool->refcnt == 0
          * which implies no work queued to the pool, which implies no worker can
          * become the manager. However a worker could have taken the role of
          * manager before the refcnts dropped to 0, since maybe_create_worker()
          * drops pool->lock
          */
         while (true) {
                 rcuwait_wait_event(&manager_wait,
                                    !(pool->flags & POOL_MANAGER_ACTIVE),
                                    TASK_UNINTERRUPTIBLE);
 
                 mutex_lock(&wq_pool_attach_mutex);
                 raw_spin_lock_irq(&pool->lock);
                 if (!(pool->flags & POOL_MANAGER_ACTIVE)) {
                         pool->flags |= POOL_MANAGER_ACTIVE;
                         break;
                 }
                 raw_spin_unlock_irq(&pool->lock);
                 mutex_unlock(&wq_pool_attach_mutex);
         }
 
         while ((worker = first_idle_worker(pool)))
                 set_worker_dying(worker, &cull_list);
         WARN_ON(pool->nr_workers || pool->nr_idle);
         raw_spin_unlock_irq(&pool->lock);
 
         detach_dying_workers(&cull_list);
 
         mutex_unlock(&wq_pool_attach_mutex);
 
         reap_dying_workers(&cull_list);
 
         /* shut down the timers */
         del_timer_sync(&pool->idle_timer);
         cancel_work_sync(&pool->idle_cull_work);
         del_timer_sync(&pool->mayday_timer);
 
         /* RCU protected to allow dereferences from get_work_pool() */
         call_rcu(&pool->rcu, rcu_free_pool);
 }
 
 /**
  * get_unbound_pool - get a worker_pool with the specified attributes
  * @attrs: the attributes of the worker_pool to get
  *
  * Obtain a worker_pool which has the same attributes as @attrs, bump the
  * reference count and return it.  If there already is a matching
  * worker_pool, it will be used; otherwise, this function attempts to
  * create a new one.
  *
  * Should be called with wq_pool_mutex held.
  *
  * Return: On success, a worker_pool with the same attributes as @attrs.
  * On failure, %NULL.
  */
 static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 {
         struct wq_pod_type *pt = &wq_pod_types[WQ_AFFN_NUMA];
         u32 hash = wqattrs_hash(attrs);
         struct worker_pool *pool;
         int pod, node = NUMA_NO_NODE;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         /* do we already have a matching pool? */
         hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
                 if (wqattrs_equal(pool->attrs, attrs)) {
                         pool->refcnt++;
                         return pool;
                 }
         }
 
         /* If __pod_cpumask is contained inside a NUMA pod, that's our node */
         for (pod = 0; pod < pt->nr_pods; pod++) {
                 if (cpumask_subset(attrs->__pod_cpumask, pt->pod_cpus[pod])) {
                         node = pt->pod_node[pod];
                         break;
                 }
         }
 
         /* nope, create a new one */
         pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, node);
         if (!pool || init_worker_pool(pool) < 0)
                 goto fail;
 
         pool->node = node;
         copy_workqueue_attrs(pool->attrs, attrs);
         wqattrs_clear_for_pool(pool->attrs);
 
         if (worker_pool_assign_id(pool) < 0)
                 goto fail;
 
         /* create and start the initial worker */
         if (wq_online && !create_worker(pool))
                 goto fail;
 
         /* install */
         hash_add(unbound_pool_hash, &pool->hash_node, hash);
 
         return pool;
 fail:
         if (pool)
                 put_unbound_pool(pool);
         return NULL;
 }
 
 /*
  * Scheduled on pwq_release_worker by put_pwq() when an unbound pwq hits zero
  * refcnt and needs to be destroyed.
  */
 static void pwq_release_workfn(struct kthread_work *work)
 {
         struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
                                                   release_work);
         struct workqueue_struct *wq = pwq->wq;
         struct worker_pool *pool = pwq->pool;
         bool is_last = false;
 
         /*
          * When @pwq is not linked, it doesn't hold any reference to the
          * @wq, and @wq is invalid to access.
          */
         if (!list_empty(&pwq->pwqs_node)) {
                 mutex_lock(&wq->mutex);
                 list_del_rcu(&pwq->pwqs_node);
                 is_last = list_empty(&wq->pwqs);
 
                 /*
                  * For ordered workqueue with a plugged dfl_pwq, restart it now.
                  */
                 if (!is_last && (wq->flags & __WQ_ORDERED))
                         unplug_oldest_pwq(wq);
 
                 mutex_unlock(&wq->mutex);
         }
 
         if (wq->flags & WQ_UNBOUND) {
                 mutex_lock(&wq_pool_mutex);
                 put_unbound_pool(pool);
                 mutex_unlock(&wq_pool_mutex);
         }
 
         if (!list_empty(&pwq->pending_node)) {
                 struct wq_node_nr_active *nna =
                         wq_node_nr_active(pwq->wq, pwq->pool->node);
 
                 raw_spin_lock_irq(&nna->lock);
                 list_del_init(&pwq->pending_node);
                 raw_spin_unlock_irq(&nna->lock);
         }
 
         kfree_rcu(pwq, rcu);
 
         /*
          * If we're the last pwq going away, @wq is already dead and no one
          * is gonna access it anymore.  Schedule RCU free.
          */
         if (is_last) {
                 wq_unregister_lockdep(wq);
                 call_rcu(&wq->rcu, rcu_free_wq);
         }
 }
 
 /* initialize newly allocated @pwq which is associated with @wq and @pool */
 static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
                      struct worker_pool *pool)
 {
         BUG_ON((unsigned long)pwq & ~WORK_STRUCT_PWQ_MASK);
 
         memset(pwq, 0, sizeof(*pwq));
 
         pwq->pool = pool;
         pwq->wq = wq;
         pwq->flush_color = -1;
         pwq->refcnt = 1;
         INIT_LIST_HEAD(&pwq->inactive_works);
         INIT_LIST_HEAD(&pwq->pending_node);
         INIT_LIST_HEAD(&pwq->pwqs_node);
         INIT_LIST_HEAD(&pwq->mayday_node);
         kthread_init_work(&pwq->release_work, pwq_release_workfn);
 }
 
 /* sync @pwq with the current state of its associated wq and link it */
 static void link_pwq(struct pool_workqueue *pwq)
 {
         struct workqueue_struct *wq = pwq->wq;
 
         lockdep_assert_held(&wq->mutex);
 
         /* may be called multiple times, ignore if already linked */
         if (!list_empty(&pwq->pwqs_node))
                 return;
 
         /* set the matching work_color */
         pwq->work_color = wq->work_color;
 
         /* link in @pwq */
         list_add_tail_rcu(&pwq->pwqs_node, &wq->pwqs);
 }
 
 /* obtain a pool matching @attr and create a pwq associating the pool and @wq */
 static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
                                         const struct workqueue_attrs *attrs)
 {
         struct worker_pool *pool;
         struct pool_workqueue *pwq;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         pool = get_unbound_pool(attrs);
         if (!pool)
                 return NULL;
 
         pwq = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL, pool->node);
         if (!pwq) {
                 put_unbound_pool(pool);
                 return NULL;
         }
 
         init_pwq(pwq, wq, pool);
         return pwq;
 }
 
 static void apply_wqattrs_lock(void)
 {
         mutex_lock(&wq_pool_mutex);
 }
 
 static void apply_wqattrs_unlock(void)
 {
         mutex_unlock(&wq_pool_mutex);
 }
 
 /**
  * wq_calc_pod_cpumask - calculate a wq_attrs' cpumask for a pod
  * @attrs: the wq_attrs of the default pwq of the target workqueue
  * @cpu: the target CPU
  *
  * Calculate the cpumask a workqueue with @attrs should use on @pod.
  * The result is stored in @attrs->__pod_cpumask.
  *
  * If pod affinity is not enabled, @attrs->cpumask is always used. If enabled
  * and @pod has online CPUs requested by @attrs, the returned cpumask is the
  * intersection of the possible CPUs of @pod and @attrs->cpumask.
  *
  * The caller is responsible for ensuring that the cpumask of @pod stays stable.
  */
 static void wq_calc_pod_cpumask(struct workqueue_attrs *attrs, int cpu)
 {
         const struct wq_pod_type *pt = wqattrs_pod_type(attrs);
         int pod = pt->cpu_pod[cpu];
 
         /* calculate possible CPUs in @pod that @attrs wants */
         cpumask_and(attrs->__pod_cpumask, pt->pod_cpus[pod], attrs->cpumask);
         /* does @pod have any online CPUs @attrs wants? */
         if (!cpumask_intersects(attrs->__pod_cpumask, wq_online_cpumask)) {
                 cpumask_copy(attrs->__pod_cpumask, attrs->cpumask);
                 return;
         }
 }
 
 /* install @pwq into @wq and return the old pwq, @cpu < 0 for dfl_pwq */
 static struct pool_workqueue *install_unbound_pwq(struct workqueue_struct *wq,
                                         int cpu, struct pool_workqueue *pwq)
 {
         struct pool_workqueue __rcu **slot = unbound_pwq_slot(wq, cpu);
         struct pool_workqueue *old_pwq;
 
         lockdep_assert_held(&wq_pool_mutex);
         lockdep_assert_held(&wq->mutex);
 
         /* link_pwq() can handle duplicate calls */
         link_pwq(pwq);
 
         old_pwq = rcu_access_pointer(*slot);
         rcu_assign_pointer(*slot, pwq);
         return old_pwq;
 }
 
 /* context to store the prepared attrs & pwqs before applying */
 struct apply_wqattrs_ctx {
         struct workqueue_struct *wq;            /* target workqueue */
         struct workqueue_attrs  *attrs;         /* attrs to apply */
         struct list_head        list;           /* queued for batching commit */
         struct pool_workqueue   *dfl_pwq;
         struct pool_workqueue   *pwq_tbl[];
 };
 
 /* free the resources after success or abort */
 static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx)
 {
         if (ctx) {
                 int cpu;
 
                 for_each_possible_cpu(cpu)
                         put_pwq_unlocked(ctx->pwq_tbl[cpu]);
                 put_pwq_unlocked(ctx->dfl_pwq);
 
                 free_workqueue_attrs(ctx->attrs);
 
                 kfree(ctx);
         }
 }
 
 /* allocate the attrs and pwqs for later installation */
 static struct apply_wqattrs_ctx *
 apply_wqattrs_prepare(struct workqueue_struct *wq,
                       const struct workqueue_attrs *attrs,
                       const cpumask_var_t unbound_cpumask)
 {
         struct apply_wqattrs_ctx *ctx;
         struct workqueue_attrs *new_attrs;
         int cpu;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         if (WARN_ON(attrs->affn_scope < 0 ||
                     attrs->affn_scope >= WQ_AFFN_NR_TYPES))
                 return ERR_PTR(-EINVAL);
 
         ctx = kzalloc(struct_size(ctx, pwq_tbl, nr_cpu_ids), GFP_KERNEL);
 
         new_attrs = alloc_workqueue_attrs();
         if (!ctx || !new_attrs)
                 goto out_free;
 
         /*
          * If something goes wrong during CPU up/down, we'll fall back to
          * the default pwq covering whole @attrs->cpumask.  Always create
          * it even if we don't use it immediately.
          */
         copy_workqueue_attrs(new_attrs, attrs);
         wqattrs_actualize_cpumask(new_attrs, unbound_cpumask);
         cpumask_copy(new_attrs->__pod_cpumask, new_attrs->cpumask);
         ctx->dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
         if (!ctx->dfl_pwq)
                 goto out_free;
 
         for_each_possible_cpu(cpu) {
                 if (new_attrs->ordered) {
                         ctx->dfl_pwq->refcnt++;
                         ctx->pwq_tbl[cpu] = ctx->dfl_pwq;
                 } else {
                         wq_calc_pod_cpumask(new_attrs, cpu);
                         ctx->pwq_tbl[cpu] = alloc_unbound_pwq(wq, new_attrs);
                         if (!ctx->pwq_tbl[cpu])
                                 goto out_free;
                 }
         }
 
         /* save the user configured attrs and sanitize it. */
         copy_workqueue_attrs(new_attrs, attrs);
         cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
         cpumask_copy(new_attrs->__pod_cpumask, new_attrs->cpumask);
         ctx->attrs = new_attrs;
 
         /*
          * For initialized ordered workqueues, there should only be one pwq
          * (dfl_pwq). Set the plugged flag of ctx->dfl_pwq to suspend execution
          * of newly queued work items until execution of older work items in
          * the old pwq's have completed.
          */
         if ((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs))
                 ctx->dfl_pwq->plugged = true;
 
         ctx->wq = wq;
         return ctx;
 
 out_free:
         free_workqueue_attrs(new_attrs);
         apply_wqattrs_cleanup(ctx);
         return ERR_PTR(-ENOMEM);
 }
 
 /* set attrs and install prepared pwqs, @ctx points to old pwqs on return */
 static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
 {
         int cpu;
 
         /* all pwqs have been created successfully, let's install'em */
         mutex_lock(&ctx->wq->mutex);
 
         copy_workqueue_attrs(ctx->wq->unbound_attrs, ctx->attrs);
 
         /* save the previous pwqs and install the new ones */
         for_each_possible_cpu(cpu)
                 ctx->pwq_tbl[cpu] = install_unbound_pwq(ctx->wq, cpu,
                                                         ctx->pwq_tbl[cpu]);
         ctx->dfl_pwq = install_unbound_pwq(ctx->wq, -1, ctx->dfl_pwq);
 
         /* update node_nr_active->max */
         wq_update_node_max_active(ctx->wq, -1);
 
         /* rescuer needs to respect wq cpumask changes */
         if (ctx->wq->rescuer)
                 set_cpus_allowed_ptr(ctx->wq->rescuer->task,
                                      unbound_effective_cpumask(ctx->wq));
 
         mutex_unlock(&ctx->wq->mutex);
 }
 
 static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
                                         const struct workqueue_attrs *attrs)
 {
         struct apply_wqattrs_ctx *ctx;
 
         /* only unbound workqueues can change attributes */
         if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
                 return -EINVAL;
 
         ctx = apply_wqattrs_prepare(wq, attrs, wq_unbound_cpumask);
         if (IS_ERR(ctx))
                 return PTR_ERR(ctx);
 
         /* the ctx has been prepared successfully, let's commit it */
         apply_wqattrs_commit(ctx);
         apply_wqattrs_cleanup(ctx);
 
         return 0;
 }
 
 /**
  * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
  * @wq: the target workqueue
  * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
  *
  * Apply @attrs to an unbound workqueue @wq. Unless disabled, this function maps
  * a separate pwq to each CPU pod with possibles CPUs in @attrs->cpumask so that
  * work items are affine to the pod it was issued on. Older pwqs are released as
  * in-flight work items finish. Note that a work item which repeatedly requeues
  * itself back-to-back will stay on its current pwq.
  *
  * Performs GFP_KERNEL allocations.
  *
  * Return: 0 on success and -errno on failure.
  */
 int apply_workqueue_attrs(struct workqueue_struct *wq,
                           const struct workqueue_attrs *attrs)
 {
         int ret;
 
         mutex_lock(&wq_pool_mutex);
         ret = apply_workqueue_attrs_locked(wq, attrs);
         mutex_unlock(&wq_pool_mutex);
 
         return ret;
 }
 
 /**
  * unbound_wq_update_pwq - update a pwq slot for CPU hot[un]plug
  * @wq: the target workqueue
  * @cpu: the CPU to update the pwq slot for
  *
  * This function is to be called from %CPU_DOWN_PREPARE, %CPU_ONLINE and
  * %CPU_DOWN_FAILED.  @cpu is in the same pod of the CPU being hot[un]plugged.
  *
  *
  * If pod affinity can't be adjusted due to memory allocation failure, it falls
  * back to @wq->dfl_pwq which may not be optimal but is always correct.
  *
  * Note that when the last allowed CPU of a pod goes offline for a workqueue
  * with a cpumask spanning multiple pods, the workers which were already
  * executing the work items for the workqueue will lose their CPU affinity and
  * may execute on any CPU. This is similar to how per-cpu workqueues behave on
  * CPU_DOWN. If a workqueue user wants strict affinity, it's the user's
  * responsibility to flush the work item from CPU_DOWN_PREPARE.
  */
 static void unbound_wq_update_pwq(struct workqueue_struct *wq, int cpu)
 {
         struct pool_workqueue *old_pwq = NULL, *pwq;
         struct workqueue_attrs *target_attrs;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         if (!(wq->flags & WQ_UNBOUND) || wq->unbound_attrs->ordered)
                 return;
 
         /*
          * We don't wanna alloc/free wq_attrs for each wq for each CPU.
          * Let's use a preallocated one.  The following buf is protected by
          * CPU hotplug exclusion.
          */
         target_attrs = unbound_wq_update_pwq_attrs_buf;
 
         copy_workqueue_attrs(target_attrs, wq->unbound_attrs);
         wqattrs_actualize_cpumask(target_attrs, wq_unbound_cpumask);
 
         /* nothing to do if the target cpumask matches the current pwq */
         wq_calc_pod_cpumask(target_attrs, cpu);
         if (wqattrs_equal(target_attrs, unbound_pwq(wq, cpu)->pool->attrs))
                 return;
 
         /* create a new pwq */
         pwq = alloc_unbound_pwq(wq, target_attrs);
         if (!pwq) {
                 pr_warn("workqueue: allocation failed while updating CPU pod affinity of \"%s\"\n",
                         wq->name);
                 goto use_dfl_pwq;
         }
 
         /* Install the new pwq. */
         mutex_lock(&wq->mutex);
         old_pwq = install_unbound_pwq(wq, cpu, pwq);
         goto out_unlock;
 
 use_dfl_pwq:
         mutex_lock(&wq->mutex);
         pwq = unbound_pwq(wq, -1);
         raw_spin_lock_irq(&pwq->pool->lock);
         get_pwq(pwq);
         raw_spin_unlock_irq(&pwq->pool->lock);
         old_pwq = install_unbound_pwq(wq, cpu, pwq);
 out_unlock:
         mutex_unlock(&wq->mutex);
         put_pwq_unlocked(old_pwq);
 }
 
 static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 {
         bool highpri = wq->flags & WQ_HIGHPRI;
         int cpu, ret;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         wq->cpu_pwq = alloc_percpu(struct pool_workqueue *);
         if (!wq->cpu_pwq)
                 goto enomem;
 
         if (!(wq->flags & WQ_UNBOUND)) {
                 struct worker_pool __percpu *pools;
 
                 if (wq->flags & WQ_BH)
                         pools = bh_worker_pools;
                 else
                         pools = cpu_worker_pools;
 
                 for_each_possible_cpu(cpu) {
                         struct pool_workqueue **pwq_p;
                         struct worker_pool *pool;
 
                         pool = &(per_cpu_ptr(pools, cpu)[highpri]);
                         pwq_p = per_cpu_ptr(wq->cpu_pwq, cpu);
 
                         *pwq_p = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL,
                                                        pool->node);
                         if (!*pwq_p)
                                 goto enomem;
 
                         init_pwq(*pwq_p, wq, pool);
 
                         mutex_lock(&wq->mutex);
                         link_pwq(*pwq_p);
                         mutex_unlock(&wq->mutex);
                 }
                 return 0;
         }
 
         if (wq->flags & __WQ_ORDERED) {
                 struct pool_workqueue *dfl_pwq;
 
                 ret = apply_workqueue_attrs_locked(wq, ordered_wq_attrs[highpri]);
                 /* there should only be single pwq for ordering guarantee */
                 dfl_pwq = rcu_access_pointer(wq->dfl_pwq);
                 WARN(!ret && (wq->pwqs.next != &dfl_pwq->pwqs_node ||
                               wq->pwqs.prev != &dfl_pwq->pwqs_node),
                      "ordering guarantee broken for workqueue %s\n", wq->name);
         } else {
                 ret = apply_workqueue_attrs_locked(wq, unbound_std_wq_attrs[highpri]);
         }
 
         return ret;
 
 enomem:
         if (wq->cpu_pwq) {
                 for_each_possible_cpu(cpu) {
                         struct pool_workqueue *pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);
 
                         if (pwq)
                                 kmem_cache_free(pwq_cache, pwq);
                 }
                 free_percpu(wq->cpu_pwq);
                 wq->cpu_pwq = NULL;
         }
         return -ENOMEM;
 }
 
 static int wq_clamp_max_active(int max_active, unsigned int flags,
                                const char *name)
 {
         if (max_active < 1 || max_active > WQ_MAX_ACTIVE)
                 pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
                         max_active, name, 1, WQ_MAX_ACTIVE);
 
         return clamp_val(max_active, 1, WQ_MAX_ACTIVE);
 }
 
 /*
  * Workqueues which may be used during memory reclaim should have a rescuer
  * to guarantee forward progress.
  */
 static int init_rescuer(struct workqueue_struct *wq)
 {
         struct worker *rescuer;
         char id_buf[WORKER_ID_LEN];
         int ret;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         if (!(wq->flags & WQ_MEM_RECLAIM))
                 return 0;
 
         rescuer = alloc_worker(NUMA_NO_NODE);
         if (!rescuer) {
                 pr_err("workqueue: Failed to allocate a rescuer for wq \"%s\"\n",
                        wq->name);
                 return -ENOMEM;
         }
 
         rescuer->rescue_wq = wq;
         format_worker_id(id_buf, sizeof(id_buf), rescuer, NULL);
 
         rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", id_buf);
         if (IS_ERR(rescuer->task)) {
                 ret = PTR_ERR(rescuer->task);
                 pr_err("workqueue: Failed to create a rescuer kthread for wq \"%s\": %pe",
                        wq->name, ERR_PTR(ret));
                 kfree(rescuer);
                 return ret;
         }
 
         wq->rescuer = rescuer;
         if (wq->flags & WQ_UNBOUND)
                 kthread_bind_mask(rescuer->task, unbound_effective_cpumask(wq));
         else
                 kthread_bind_mask(rescuer->task, cpu_possible_mask);
         wake_up_process(rescuer->task);
 
         return 0;
 }
 
 /**
  * wq_adjust_max_active - update a wq's max_active to the current setting
  * @wq: target workqueue
  *
  * If @wq isn't freezing, set @wq->max_active to the saved_max_active and
  * activate inactive work items accordingly. If @wq is freezing, clear
  * @wq->max_active to zero.
  */
 static void wq_adjust_max_active(struct workqueue_struct *wq)
 {
         bool activated;
         int new_max, new_min;
 
         lockdep_assert_held(&wq->mutex);
 
         if ((wq->flags & WQ_FREEZABLE) && workqueue_freezing) {
                 new_max = 0;
                 new_min = 0;
         } else {
                 new_max = wq->saved_max_active;
                 new_min = wq->saved_min_active;
         }
 
         if (wq->max_active == new_max && wq->min_active == new_min)
                 return;
 
         /*
          * Update @wq->max/min_active and then kick inactive work items if more
          * active work items are allowed. This doesn't break work item ordering
          * because new work items are always queued behind existing inactive
          * work items if there are any.
          */
         WRITE_ONCE(wq->max_active, new_max);
         WRITE_ONCE(wq->min_active, new_min);
 
         if (wq->flags & WQ_UNBOUND)
                 wq_update_node_max_active(wq, -1);
 
         if (new_max == 0)
                 return;
 
         /*
          * Round-robin through pwq's activating the first inactive work item
          * until max_active is filled.
          */
         do {
                 struct pool_workqueue *pwq;
 
                 activated = false;
                 for_each_pwq(pwq, wq) {
                         unsigned long irq_flags;
 
                         /* can be called during early boot w/ irq disabled */
                         raw_spin_lock_irqsave(&pwq->pool->lock, irq_flags);
                         if (pwq_activate_first_inactive(pwq, true)) {
                                 activated = true;
                                 kick_pool(pwq->pool);
                         }
                         raw_spin_unlock_irqrestore(&pwq->pool->lock, irq_flags);
                 }
         } while (activated);
 }
 
 __printf(1, 4)
 struct workqueue_struct *alloc_workqueue(const char *fmt,
                                          unsigned int flags,
                                          int max_active, ...)
 {
         va_list args;
         struct workqueue_struct *wq;
         size_t wq_size;
         int name_len;
 
         if (flags & WQ_BH) {
                 if (WARN_ON_ONCE(flags & ~__WQ_BH_ALLOWS))
                         return NULL;
                 if (WARN_ON_ONCE(max_active))
                         return NULL;
         }
 
         /* see the comment above the definition of WQ_POWER_EFFICIENT */
         if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
                 flags |= WQ_UNBOUND;
 
         /* allocate wq and format name */
         if (flags & WQ_UNBOUND)
                 wq_size = struct_size(wq, node_nr_active, nr_node_ids + 1);
         else
                 wq_size = sizeof(*wq);
 
         wq = kzalloc(wq_size, GFP_KERNEL);
         if (!wq)
                 return NULL;
 
         if (flags & WQ_UNBOUND) {
                 wq->unbound_attrs = alloc_workqueue_attrs();
                 if (!wq->unbound_attrs)
                         goto err_free_wq;
         }
 
         va_start(args, max_active);
         name_len = vsnprintf(wq->name, sizeof(wq->name), fmt, args);
         va_end(args);
 
         if (name_len >= WQ_NAME_LEN)
                 pr_warn_once("workqueue: name exceeds WQ_NAME_LEN. Truncating to: %s\n",
                              wq->name);
 
         if (flags & WQ_BH) {
                 /*
                  * BH workqueues always share a single execution context per CPU
                  * and don't impose any max_active limit.
                  */
                 max_active = INT_MAX;
         } else {
                 max_active = max_active ?: WQ_DFL_ACTIVE;
                 max_active = wq_clamp_max_active(max_active, flags, wq->name);
         }
 
         /* init wq */
         wq->flags = flags;
         wq->max_active = max_active;
         wq->min_active = min(max_active, WQ_DFL_MIN_ACTIVE);
         wq->saved_max_active = wq->max_active;
         wq->saved_min_active = wq->min_active;
         mutex_init(&wq->mutex);
         atomic_set(&wq->nr_pwqs_to_flush, 0);
         INIT_LIST_HEAD(&wq->pwqs);
         INIT_LIST_HEAD(&wq->flusher_queue);
         INIT_LIST_HEAD(&wq->flusher_overflow);
         INIT_LIST_HEAD(&wq->maydays);
 
         wq_init_lockdep(wq);
         INIT_LIST_HEAD(&wq->list);
 
         if (flags & WQ_UNBOUND) {
                 if (alloc_node_nr_active(wq->node_nr_active) < 0)
                         goto err_unreg_lockdep;
         }
 
         /*
          * wq_pool_mutex protects the workqueues list, allocations of PWQs,
          * and the global freeze state.
          */
         apply_wqattrs_lock();
 
         if (alloc_and_link_pwqs(wq) < 0)
                 goto err_unlock_free_node_nr_active;
 
         mutex_lock(&wq->mutex);
         wq_adjust_max_active(wq);
         mutex_unlock(&wq->mutex);
 
         list_add_tail_rcu(&wq->list, &workqueues);
 
         if (wq_online && init_rescuer(wq) < 0)
                 goto err_unlock_destroy;
 
         apply_wqattrs_unlock();
 
         if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
                 goto err_destroy;
 
         return wq;
 
 err_unlock_free_node_nr_active:
         apply_wqattrs_unlock();
         /*
          * Failed alloc_and_link_pwqs() may leave pending pwq->release_work,
          * flushing the pwq_release_worker ensures that the pwq_release_workfn()
          * completes before calling kfree(wq).
          */
         if (wq->flags & WQ_UNBOUND) {
                 kthread_flush_worker(pwq_release_worker);
                 free_node_nr_active(wq->node_nr_active);
         }
 err_unreg_lockdep:
         wq_unregister_lockdep(wq);
         wq_free_lockdep(wq);
 err_free_wq:
         free_workqueue_attrs(wq->unbound_attrs);
         kfree(wq);
         return NULL;
 err_unlock_destroy:
         apply_wqattrs_unlock();
 err_destroy:
         destroy_workqueue(wq);
         return NULL;
 }
 EXPORT_SYMBOL_GPL(alloc_workqueue);
 
 static bool pwq_busy(struct pool_workqueue *pwq)
 {
         int i;
 
         for (i = 0; i < WORK_NR_COLORS; i++)
                 if (pwq->nr_in_flight[i])
                         return true;
 
         if ((pwq != rcu_access_pointer(pwq->wq->dfl_pwq)) && (pwq->refcnt > 1))
                 return true;
         if (!pwq_is_empty(pwq))
                 return true;
 
         return false;
 }
 
 /**
  * destroy_workqueue - safely terminate a workqueue
  * @wq: target workqueue
  *
  * Safely destroy a workqueue. All work currently pending will be done first.
  */
 void destroy_workqueue(struct workqueue_struct *wq)
 {
         struct pool_workqueue *pwq;
         int cpu;
 
         /*
          * Remove it from sysfs first so that sanity check failure doesn't
          * lead to sysfs name conflicts.
          */
         workqueue_sysfs_unregister(wq);
 
         /* mark the workqueue destruction is in progress */
         mutex_lock(&wq->mutex);
         wq->flags |= __WQ_DESTROYING;
         mutex_unlock(&wq->mutex);
 
         /* drain it before proceeding with destruction */
         drain_workqueue(wq);
 
         /* kill rescuer, if sanity checks fail, leave it w/o rescuer */
         if (wq->rescuer) {
                 struct worker *rescuer = wq->rescuer;
 
                 /* this prevents new queueing */
                 raw_spin_lock_irq(&wq_mayday_lock);
                 wq->rescuer = NULL;
                 raw_spin_unlock_irq(&wq_mayday_lock);
 
                 /* rescuer will empty maydays list before exiting */
                 kthread_stop(rescuer->task);
                 kfree(rescuer);
         }
 
         /*
          * Sanity checks - grab all the locks so that we wait for all
          * in-flight operations which may do put_pwq().
          */
         mutex_lock(&wq_pool_mutex);
         mutex_lock(&wq->mutex);
         for_each_pwq(pwq, wq) {
                 raw_spin_lock_irq(&pwq->pool->lock);
                 if (WARN_ON(pwq_busy(pwq))) {
                         pr_warn("%s: %s has the following busy pwq\n",
                                 __func__, wq->name);
                         show_pwq(pwq);
                         raw_spin_unlock_irq(&pwq->pool->lock);
                         mutex_unlock(&wq->mutex);
                         mutex_unlock(&wq_pool_mutex);
                         show_one_workqueue(wq);
                         return;
                 }
                 raw_spin_unlock_irq(&pwq->pool->lock);
         }
         mutex_unlock(&wq->mutex);
 
         /*
          * wq list is used to freeze wq, remove from list after
          * flushing is complete in case freeze races us.
          */
         list_del_rcu(&wq->list);
         mutex_unlock(&wq_pool_mutex);
 
         /*
          * We're the sole accessor of @wq. Directly access cpu_pwq and dfl_pwq
          * to put the base refs. @wq will be auto-destroyed from the last
          * pwq_put. RCU read lock prevents @wq from going away from under us.
          */
         rcu_read_lock();
 
         for_each_possible_cpu(cpu) {
                 put_pwq_unlocked(unbound_pwq(wq, cpu));
                 RCU_INIT_POINTER(*unbound_pwq_slot(wq, cpu), NULL);
         }
 
         put_pwq_unlocked(unbound_pwq(wq, -1));
         RCU_INIT_POINTER(*unbound_pwq_slot(wq, -1), NULL);
 
         rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(destroy_workqueue);
 
 /**
  * workqueue_set_max_active - adjust max_active of a workqueue
  * @wq: target workqueue
  * @max_active: new max_active value.
  *
  * Set max_active of @wq to @max_active. See the alloc_workqueue() function
  * comment.
  *
  * CONTEXT:
  * Don't call from IRQ context.
  */
 void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 {
         /* max_active doesn't mean anything for BH workqueues */
         if (WARN_ON(wq->flags & WQ_BH))
                 return;
         /* disallow meddling with max_active for ordered workqueues */
         if (WARN_ON(wq->flags & __WQ_ORDERED))
                 return;
 
         max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
 
         mutex_lock(&wq->mutex);
 
         wq->saved_max_active = max_active;
         if (wq->flags & WQ_UNBOUND)
                 wq->saved_min_active = min(wq->saved_min_active, max_active);
 
         wq_adjust_max_active(wq);
 
         mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL_GPL(workqueue_set_max_active);
 
 /**
  * workqueue_set_min_active - adjust min_active of an unbound workqueue
  * @wq: target unbound workqueue
  * @min_active: new min_active value
  *
  * Set min_active of an unbound workqueue. Unlike other types of workqueues, an
  * unbound workqueue is not guaranteed to be able to process max_active
  * interdependent work items. Instead, an unbound workqueue is guaranteed to be
  * able to process min_active number of interdependent work items which is
  * %WQ_DFL_MIN_ACTIVE by default.
  *
  * Use this function to adjust the min_active value between 0 and the current
  * max_active.
  */
 void workqueue_set_min_active(struct workqueue_struct *wq, int min_active)
 {
         /* min_active is only meaningful for non-ordered unbound workqueues */
         if (WARN_ON((wq->flags & (WQ_BH | WQ_UNBOUND | __WQ_ORDERED)) !=
                     WQ_UNBOUND))
                 return;
 
         mutex_lock(&wq->mutex);
         wq->saved_min_active = clamp(min_active, 0, wq->saved_max_active);
         wq_adjust_max_active(wq);
         mutex_unlock(&wq->mutex);
 }
 
 /**
  * current_work - retrieve %current task's work struct
  *
  * Determine if %current task is a workqueue worker and what it's working on.
  * Useful to find out the context that the %current task is running in.
  *
  * Return: work struct if %current task is a workqueue worker, %NULL otherwise.
  */
 struct work_struct *current_work(void)
 {
         struct worker *worker = current_wq_worker();
 
         return worker ? worker->current_work : NULL;
 }
 EXPORT_SYMBOL(current_work);
 
 /**
  * current_is_workqueue_rescuer - is %current workqueue rescuer?
  *
  * Determine whether %current is a workqueue rescuer.  Can be used from
  * work functions to determine whether it's being run off the rescuer task.
  *
  * Return: %true if %current is a workqueue rescuer. %false otherwise.
  */
 bool current_is_workqueue_rescuer(void)
 {
         struct worker *worker = current_wq_worker();
 
         return worker && worker->rescue_wq;
 }
 
 /**
  * workqueue_congested - test whether a workqueue is congested
  * @cpu: CPU in question
  * @wq: target workqueue
  *
  * Test whether @wq's cpu workqueue for @cpu is congested.  There is
  * no synchronization around this function and the test result is
  * unreliable and only useful as advisory hints or for debugging.
  *
  * If @cpu is WORK_CPU_UNBOUND, the test is performed on the local CPU.
  *
  * With the exception of ordered workqueues, all workqueues have per-cpu
  * pool_workqueues, each with its own congested state. A workqueue being
  * congested on one CPU doesn't mean that the workqueue is contested on any
  * other CPUs.
  *
  * Return:
  * %true if congested, %false otherwise.
  */
 bool workqueue_congested(int cpu, struct workqueue_struct *wq)
 {
         struct pool_workqueue *pwq;
         bool ret;
 
         rcu_read_lock();
         preempt_disable();
 
         if (cpu == WORK_CPU_UNBOUND)
                 cpu = smp_processor_id();
 
         pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);
         ret = !list_empty(&pwq->inactive_works);
 
         preempt_enable();
         rcu_read_unlock();
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(workqueue_congested);
 
 /**
  * work_busy - test whether a work is currently pending or running
  * @work: the work to be tested
  *
  * Test whether @work is currently pending or running.  There is no
  * synchronization around this function and the test result is
  * unreliable and only useful as advisory hints or for debugging.
  *
  * Return:
  * OR'd bitmask of WORK_BUSY_* bits.
  */
 unsigned int work_busy(struct work_struct *work)
 {
         struct worker_pool *pool;
         unsigned long irq_flags;
         unsigned int ret = 0;
 
         if (work_pending(work))
                 ret |= WORK_BUSY_PENDING;
 
         rcu_read_lock();
         pool = get_work_pool(work);
         if (pool) {
                 raw_spin_lock_irqsave(&pool->lock, irq_flags);
                 if (find_worker_executing_work(pool, work))
                         ret |= WORK_BUSY_RUNNING;
                 raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
         }
         rcu_read_unlock();
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(work_busy);
 
 /**
  * set_worker_desc - set description for the current work item
  * @fmt: printf-style format string
  * @...: arguments for the format string
  *
  * This function can be called by a running work function to describe what
  * the work item is about.  If the worker task gets dumped, this
  * information will be printed out together to help debugging.  The
  * description can be at most WORKER_DESC_LEN including the trailing '\0'.
  */
 void set_worker_desc(const char *fmt, ...)
 {
         struct worker *worker = current_wq_worker();
         va_list args;
 
         if (worker) {
                 va_start(args, fmt);
                 vsnprintf(worker->desc, sizeof(worker->desc), fmt, args);
                 va_end(args);
         }
 }
 EXPORT_SYMBOL_GPL(set_worker_desc);
 
 /**
  * print_worker_info - print out worker information and description
  * @log_lvl: the log level to use when printing
  * @task: target task
  *
  * If @task is a worker and currently executing a work item, print out the
  * name of the workqueue being serviced and worker description set with
  * set_worker_desc() by the currently executing work item.
  *
  * This function can be safely called on any task as long as the
  * task_struct itself is accessible.  While safe, this function isn't
  * synchronized and may print out mixups or garbages of limited length.
  */
 void print_worker_info(const char *log_lvl, struct task_struct *task)
 {
         work_func_t *fn = NULL;
         char name[WQ_NAME_LEN] = { };
         char desc[WORKER_DESC_LEN] = { };
         struct pool_workqueue *pwq = NULL;
         struct workqueue_struct *wq = NULL;
         struct worker *worker;
 
         if (!(task->flags & PF_WQ_WORKER))
                 return;
 
         /*
          * This function is called without any synchronization and @task
          * could be in any state.  Be careful with dereferences.
          */
         worker = kthread_probe_data(task);
 
         /*
          * Carefully copy the associated workqueue's workfn, name and desc.
          * Keep the original last '\0' in case the original is garbage.
          */
         copy_from_kernel_nofault(&fn, &worker->current_func, sizeof(fn));
         copy_from_kernel_nofault(&pwq, &worker->current_pwq, sizeof(pwq));
         copy_from_kernel_nofault(&wq, &pwq->wq, sizeof(wq));
         copy_from_kernel_nofault(name, wq->name, sizeof(name) - 1);
         copy_from_kernel_nofault(desc, worker->desc, sizeof(desc) - 1);
 
         if (fn || name[0] || desc[0]) {
                 printk("%sWorkqueue: %s %ps", log_lvl, name, fn);
                 if (strcmp(name, desc))
                         pr_cont(" (%s)", desc);
                 pr_cont("\n");
         }
 }
 
 static void pr_cont_pool_info(struct worker_pool *pool)
 {
         pr_cont(" cpus=%*pbl", nr_cpumask_bits, pool->attrs->cpumask);
         if (pool->node != NUMA_NO_NODE)
                 pr_cont(" node=%d", pool->node);
         pr_cont(" flags=0x%x", pool->flags);
         if (pool->flags & POOL_BH)
                 pr_cont(" bh%s",
                         pool->attrs->nice == HIGHPRI_NICE_LEVEL ? "-hi" : "");
         else
                 pr_cont(" nice=%d", pool->attrs->nice);
 }
 
 static void pr_cont_worker_id(struct worker *worker)
 {
         struct worker_pool *pool = worker->pool;
 
         if (pool->flags & WQ_BH)
                 pr_cont("bh%s",
                         pool->attrs->nice == HIGHPRI_NICE_LEVEL ? "-hi" : "");
         else
                 pr_cont("%d%s", task_pid_nr(worker->task),
                         worker->rescue_wq ? "(RESCUER)" : "");
 }
 
 struct pr_cont_work_struct {
         bool comma;
         work_func_t func;
         long ctr;
 };
 
 static void pr_cont_work_flush(bool comma, work_func_t func, struct pr_cont_work_struct *pcwsp)
 {
         if (!pcwsp->ctr)
                 goto out_record;
         if (func == pcwsp->func) {
                 pcwsp->ctr++;
                 return;
         }
         if (pcwsp->ctr == 1)
                 pr_cont("%s %ps", pcwsp->comma ? "," : "", pcwsp->func);
         else
                 pr_cont("%s %ld*%ps", pcwsp->comma ? "," : "", pcwsp->ctr, pcwsp->func);
         pcwsp->ctr = 0;
 out_record:
         if ((long)func == -1L)
                 return;
         pcwsp->comma = comma;
         pcwsp->func = func;
         pcwsp->ctr = 1;
 }
 
 static void pr_cont_work(bool comma, struct work_struct *work, struct pr_cont_work_struct *pcwsp)
 {
         if (work->func == wq_barrier_func) {
                 struct wq_barrier *barr;
 
                 barr = container_of(work, struct wq_barrier, work);
 
                 pr_cont_work_flush(comma, (work_func_t)-1, pcwsp);
                 pr_cont("%s BAR(%d)", comma ? "," : "",
                         task_pid_nr(barr->task));
         } else {
                 if (!comma)
                         pr_cont_work_flush(comma, (work_func_t)-1, pcwsp);
                 pr_cont_work_flush(comma, work->func, pcwsp);
         }
 }
 
 static void show_pwq(struct pool_workqueue *pwq)
 {
         struct pr_cont_work_struct pcws = { .ctr = 0, };
         struct worker_pool *pool = pwq->pool;
         struct work_struct *work;
         struct worker *worker;
         bool has_in_flight = false, has_pending = false;
         int bkt;
 
         pr_info("  pwq %d:", pool->id);
         pr_cont_pool_info(pool);
 
         pr_cont(" active=%d refcnt=%d%s\n",
                 pwq->nr_active, pwq->refcnt,
                 !list_empty(&pwq->mayday_node) ? " MAYDAY" : "");
 
         hash_for_each(pool->busy_hash, bkt, worker, hentry) {
                 if (worker->current_pwq == pwq) {
                         has_in_flight = true;
                         break;
                 }
         }
         if (has_in_flight) {
                 bool comma = false;
 
                 pr_info("    in-flight:");
                 hash_for_each(pool->busy_hash, bkt, worker, hentry) {
                         if (worker->current_pwq != pwq)
                                 continue;
 
                         pr_cont(" %s", comma ? "," : "");
                         pr_cont_worker_id(worker);
                         pr_cont(":%ps", worker->current_func);
                         list_for_each_entry(work, &worker->scheduled, entry)
                                 pr_cont_work(false, work, &pcws);
                         pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
                         comma = true;
                 }
                 pr_cont("\n");
         }
 
         list_for_each_entry(work, &pool->worklist, entry) {
                 if (get_work_pwq(work) == pwq) {
                         has_pending = true;
                         break;
                 }
         }
         if (has_pending) {
                 bool comma = false;
 
                 pr_info("    pending:");
                 list_for_each_entry(work, &pool->worklist, entry) {
                         if (get_work_pwq(work) != pwq)
                                 continue;
 
                         pr_cont_work(comma, work, &pcws);
                         comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
                 }
                 pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
                 pr_cont("\n");
         }
 
         if (!list_empty(&pwq->inactive_works)) {
                 bool comma = false;
 
                 pr_info("    inactive:");
                 list_for_each_entry(work, &pwq->inactive_works, entry) {
                         pr_cont_work(comma, work, &pcws);
                         comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
                 }
                 pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
                 pr_cont("\n");
         }
 }
 
 /**
  * show_one_workqueue - dump state of specified workqueue
  * @wq: workqueue whose state will be printed
  */
 void show_one_workqueue(struct workqueue_struct *wq)
 {
         struct pool_workqueue *pwq;
         bool idle = true;
         unsigned long irq_flags;
 
         for_each_pwq(pwq, wq) {
                 if (!pwq_is_empty(pwq)) {
                         idle = false;
                         break;
                 }
         }
         if (idle) /* Nothing to print for idle workqueue */
                 return;
 
         pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);
 
         for_each_pwq(pwq, wq) {
                 raw_spin_lock_irqsave(&pwq->pool->lock, irq_flags);
                 if (!pwq_is_empty(pwq)) {
                         /*
                          * Defer printing to avoid deadlocks in console
                          * drivers that queue work while holding locks
                          * also taken in their write paths.
                          */
                         printk_deferred_enter();
                         show_pwq(pwq);
                         printk_deferred_exit();
                 }
                 raw_spin_unlock_irqrestore(&pwq->pool->lock, irq_flags);
                 /*
                  * We could be printing a lot from atomic context, e.g.
                  * sysrq-t -> show_all_workqueues(). Avoid triggering
                  * hard lockup.
                  */
                 touch_nmi_watchdog();
         }
 
 }
 
 /**
  * show_one_worker_pool - dump state of specified worker pool
  * @pool: worker pool whose state will be printed
  */
 static void show_one_worker_pool(struct worker_pool *pool)
 {
         struct worker *worker;
         bool first = true;
         unsigned long irq_flags;
         unsigned long hung = 0;
 
         raw_spin_lock_irqsave(&pool->lock, irq_flags);
         if (pool->nr_workers == pool->nr_idle)
                 goto next_pool;
 
         /* How long the first pending work is waiting for a worker. */
         if (!list_empty(&pool->worklist))
                 hung = jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000;
 
         /*
          * Defer printing to avoid deadlocks in console drivers that
          * queue work while holding locks also taken in their write
          * paths.
          */
         printk_deferred_enter();
         pr_info("pool %d:", pool->id);
         pr_cont_pool_info(pool);
         pr_cont(" hung=%lus workers=%d", hung, pool->nr_workers);
         if (pool->manager)
                 pr_cont(" manager: %d",
                         task_pid_nr(pool->manager->task));
         list_for_each_entry(worker, &pool->idle_list, entry) {
                 pr_cont(" %s", first ? "idle: " : "");
                 pr_cont_worker_id(worker);
                 first = false;
         }
         pr_cont("\n");
         printk_deferred_exit();
 next_pool:
         raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
         /*
          * We could be printing a lot from atomic context, e.g.
          * sysrq-t -> show_all_workqueues(). Avoid triggering
          * hard lockup.
          */
         touch_nmi_watchdog();
 
 }
 
 /**
  * show_all_workqueues - dump workqueue state
  *
  * Called from a sysrq handler and prints out all busy workqueues and pools.
  */
 void show_all_workqueues(void)
 {
         struct workqueue_struct *wq;
         struct worker_pool *pool;
         int pi;
 
         rcu_read_lock();
 
         pr_info("Showing busy workqueues and worker pools:\n");
 
         list_for_each_entry_rcu(wq, &workqueues, list)
                 show_one_workqueue(wq);
 
         for_each_pool(pool, pi)
                 show_one_worker_pool(pool);
 
         rcu_read_unlock();
 }
 
 /**
  * show_freezable_workqueues - dump freezable workqueue state
  *
  * Called from try_to_freeze_tasks() and prints out all freezable workqueues
  * still busy.
  */
 void show_freezable_workqueues(void)
 {
         struct workqueue_struct *wq;
 
         rcu_read_lock();
 
         pr_info("Showing freezable workqueues that are still busy:\n");
 
         list_for_each_entry_rcu(wq, &workqueues, list) {
                 if (!(wq->flags & WQ_FREEZABLE))
                         continue;
                 show_one_workqueue(wq);
         }
 
         rcu_read_unlock();
 }
 
 /* used to show worker information through /proc/PID/{comm,stat,status} */
 void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
 {
         /* stabilize PF_WQ_WORKER and worker pool association */
         mutex_lock(&wq_pool_attach_mutex);
 
         if (task->flags & PF_WQ_WORKER) {
                 struct worker *worker = kthread_data(task);
                 struct worker_pool *pool = worker->pool;
                 int off;
 
                 off = format_worker_id(buf, size, worker, pool);
 
                 if (pool) {
                         raw_spin_lock_irq(&pool->lock);
                         /*
                          * ->desc tracks information (wq name or
                          * set_worker_desc()) for the latest execution.  If
                          * current, prepend '+', otherwise '-'.
                          */
                         if (worker->desc[0] != '\0') {
                                 if (worker->current_work)
                                         scnprintf(buf + off, size - off, "+%s",
                                                   worker->desc);
                                 else
                                         scnprintf(buf + off, size - off, "-%s",
                                                   worker->desc);
                         }
                         raw_spin_unlock_irq(&pool->lock);
                 }
         } else {
                 strscpy(buf, task->comm, size);
         }
 
         mutex_unlock(&wq_pool_attach_mutex);
 }
 
 #ifdef CONFIG_SMP
 
 /*
  * CPU hotplug.
  *
  * There are two challenges in supporting CPU hotplug.  Firstly, there
  * are a lot of assumptions on strong associations among work, pwq and
  * pool which make migrating pending and scheduled works very
  * difficult to implement without impacting hot paths.  Secondly,
  * worker pools serve mix of short, long and very long running works making
  * blocked draining impractical.
  *
  * This is solved by allowing the pools to be disassociated from the CPU
  * running as an unbound one and allowing it to be reattached later if the
  * cpu comes back online.
  */
 
 static void unbind_workers(int cpu)
 {
         struct worker_pool *pool;
         struct worker *worker;
 
         for_each_cpu_worker_pool(pool, cpu) {
                 mutex_lock(&wq_pool_attach_mutex);
                 raw_spin_lock_irq(&pool->lock);
 
                 /*
                  * We've blocked all attach/detach operations. Make all workers
                  * unbound and set DISASSOCIATED.  Before this, all workers
                  * must be on the cpu.  After this, they may become diasporas.
                  * And the preemption disabled section in their sched callbacks
                  * are guaranteed to see WORKER_UNBOUND since the code here
                  * is on the same cpu.
                  */
                 for_each_pool_worker(worker, pool)
                         worker->flags |= WORKER_UNBOUND;
 
                 pool->flags |= POOL_DISASSOCIATED;
 
                 /*
                  * The handling of nr_running in sched callbacks are disabled
                  * now.  Zap nr_running.  After this, nr_running stays zero and
                  * need_more_worker() and keep_working() are always true as
                  * long as the worklist is not empty.  This pool now behaves as
                  * an unbound (in terms of concurrency management) pool which
                  * are served by workers tied to the pool.
                  */
                 pool->nr_running = 0;
 
                 /*
                  * With concurrency management just turned off, a busy
                  * worker blocking could lead to lengthy stalls.  Kick off
                  * unbound chain execution of currently pending work items.
                  */
                 kick_pool(pool);
 
                 raw_spin_unlock_irq(&pool->lock);
 
                 for_each_pool_worker(worker, pool)
                         unbind_worker(worker);
 
                 mutex_unlock(&wq_pool_attach_mutex);
         }
 }
 
 /**
  * rebind_workers - rebind all workers of a pool to the associated CPU
  * @pool: pool of interest
  *
  * @pool->cpu is coming online.  Rebind all workers to the CPU.
  */
 static void rebind_workers(struct worker_pool *pool)
 {
         struct worker *worker;
 
         lockdep_assert_held(&wq_pool_attach_mutex);
 
         /*
          * Restore CPU affinity of all workers.  As all idle workers should
          * be on the run-queue of the associated CPU before any local
          * wake-ups for concurrency management happen, restore CPU affinity
          * of all workers first and then clear UNBOUND.  As we're called
          * from CPU_ONLINE, the following shouldn't fail.
          */
         for_each_pool_worker(worker, pool) {
                 kthread_set_per_cpu(worker->task, pool->cpu);
                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
                                                   pool_allowed_cpus(pool)) < 0);
         }
 
         raw_spin_lock_irq(&pool->lock);
 
         pool->flags &= ~POOL_DISASSOCIATED;
 
         for_each_pool_worker(worker, pool) {
                 unsigned int worker_flags = worker->flags;
 
                 /*
                  * We want to clear UNBOUND but can't directly call
                  * worker_clr_flags() or adjust nr_running.  Atomically
                  * replace UNBOUND with another NOT_RUNNING flag REBOUND.
                  * @worker will clear REBOUND using worker_clr_flags() when
                  * it initiates the next execution cycle thus restoring
                  * concurrency management.  Note that when or whether
                  * @worker clears REBOUND doesn't affect correctness.
                  *
                  * WRITE_ONCE() is necessary because @worker->flags may be
                  * tested without holding any lock in
                  * wq_worker_running().  Without it, NOT_RUNNING test may
                  * fail incorrectly leading to premature concurrency
                  * management operations.
                  */
                 WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
                 worker_flags |= WORKER_REBOUND;
                 worker_flags &= ~WORKER_UNBOUND;
                 WRITE_ONCE(worker->flags, worker_flags);
         }
 
         raw_spin_unlock_irq(&pool->lock);
 }
 
 /**
  * restore_unbound_workers_cpumask - restore cpumask of unbound workers
  * @pool: unbound pool of interest
  * @cpu: the CPU which is coming up
  *
  * An unbound pool may end up with a cpumask which doesn't have any online
  * CPUs.  When a worker of such pool get scheduled, the scheduler resets
  * its cpus_allowed.  If @cpu is in @pool's cpumask which didn't have any
  * online CPU before, cpus_allowed of all its workers should be restored.
  */
 static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
 {
         static cpumask_t cpumask;
         struct worker *worker;
 
         lockdep_assert_held(&wq_pool_attach_mutex);
 
         /* is @cpu allowed for @pool? */
         if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
                 return;
 
         cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);
 
         /* as we're called from CPU_ONLINE, the following shouldn't fail */
         for_each_pool_worker(worker, pool)
                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, &cpumask) < 0);
 }
 
 int workqueue_prepare_cpu(unsigned int cpu)
 {
         struct worker_pool *pool;
 
         for_each_cpu_worker_pool(pool, cpu) {
                 if (pool->nr_workers)
                         continue;
                 if (!create_worker(pool))
                         return -ENOMEM;
         }
         return 0;
 }
 
 int workqueue_online_cpu(unsigned int cpu)
 {
         struct worker_pool *pool;
         struct workqueue_struct *wq;
         int pi;
 
         mutex_lock(&wq_pool_mutex);
 
         cpumask_set_cpu(cpu, wq_online_cpumask);
 
         for_each_pool(pool, pi) {
                 /* BH pools aren't affected by hotplug */
                 if (pool->flags & POOL_BH)
                         continue;
 
                 mutex_lock(&wq_pool_attach_mutex);
                 if (pool->cpu == cpu)
                         rebind_workers(pool);
                 else if (pool->cpu < 0)
                         restore_unbound_workers_cpumask(pool, cpu);
                 mutex_unlock(&wq_pool_attach_mutex);
         }
 
         /* update pod affinity of unbound workqueues */
         list_for_each_entry(wq, &workqueues, list) {
                 struct workqueue_attrs *attrs = wq->unbound_attrs;
 
                 if (attrs) {
                         const struct wq_pod_type *pt = wqattrs_pod_type(attrs);
                         int tcpu;
 
                         for_each_cpu(tcpu, pt->pod_cpus[pt->cpu_pod[cpu]])
                                 unbound_wq_update_pwq(wq, tcpu);
 
                         mutex_lock(&wq->mutex);
                         wq_update_node_max_active(wq, -1);
                         mutex_unlock(&wq->mutex);
                 }
         }
 
         mutex_unlock(&wq_pool_mutex);
         return 0;
 }
 
 int workqueue_offline_cpu(unsigned int cpu)
 {
         struct workqueue_struct *wq;
 
         /* unbinding per-cpu workers should happen on the local CPU */
         if (WARN_ON(cpu != smp_processor_id()))
                 return -1;
 
         unbind_workers(cpu);
 
         /* update pod affinity of unbound workqueues */
         mutex_lock(&wq_pool_mutex);
 
         cpumask_clear_cpu(cpu, wq_online_cpumask);
 
         list_for_each_entry(wq, &workqueues, list) {
                 struct workqueue_attrs *attrs = wq->unbound_attrs;
 
                 if (attrs) {
                         const struct wq_pod_type *pt = wqattrs_pod_type(attrs);
                         int tcpu;
 
                         for_each_cpu(tcpu, pt->pod_cpus[pt->cpu_pod[cpu]])
                                 unbound_wq_update_pwq(wq, tcpu);
 
                         mutex_lock(&wq->mutex);
                         wq_update_node_max_active(wq, cpu);
                         mutex_unlock(&wq->mutex);
                 }
         }
         mutex_unlock(&wq_pool_mutex);
 
         return 0;
 }
 
 struct work_for_cpu {
         struct work_struct work;
         long (*fn)(void *);
         void *arg;
         long ret;
 };
 
 static void work_for_cpu_fn(struct work_struct *work)
 {
         struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);
 
         wfc->ret = wfc->fn(wfc->arg);
 }
 
 /**
  * work_on_cpu_key - run a function in thread context on a particular cpu
  * @cpu: the cpu to run on
  * @fn: the function to run
  * @arg: the function arg
  * @key: The lock class key for lock debugging purposes
  *
  * It is up to the caller to ensure that the cpu doesn't go offline.
  * The caller must not hold any locks which would prevent @fn from completing.
  *
  * Return: The value @fn returns.
  */
 long work_on_cpu_key(int cpu, long (*fn)(void *),
                      void *arg, struct lock_class_key *key)
 {
         struct work_for_cpu wfc = { .fn = fn, .arg = arg };
 
         INIT_WORK_ONSTACK_KEY(&wfc.work, work_for_cpu_fn, key);
         schedule_work_on(cpu, &wfc.work);
         flush_work(&wfc.work);
         destroy_work_on_stack(&wfc.work);
         return wfc.ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu_key);
 
 /**
  * work_on_cpu_safe_key - run a function in thread context on a particular cpu
  * @cpu: the cpu to run on
  * @fn:  the function to run
  * @arg: the function argument
  * @key: The lock class key for lock debugging purposes
  *
  * Disables CPU hotplug and calls work_on_cpu(). The caller must not hold
  * any locks which would prevent @fn from completing.
  *
  * Return: The value @fn returns.
  */
 long work_on_cpu_safe_key(int cpu, long (*fn)(void *),
                           void *arg, struct lock_class_key *key)
 {
         long ret = -ENODEV;
 
         cpus_read_lock();
         if (cpu_online(cpu))
                 ret = work_on_cpu_key(cpu, fn, arg, key);
         cpus_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu_safe_key);
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_FREEZER
 
 /**
  * freeze_workqueues_begin - begin freezing workqueues
  *
  * Start freezing workqueues.  After this function returns, all freezable
  * workqueues will queue new works to their inactive_works list instead of
  * pool->worklist.
  *
  * CONTEXT:
  * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
  */
 void freeze_workqueues_begin(void)
 {
         struct workqueue_struct *wq;
 
         mutex_lock(&wq_pool_mutex);
 
         WARN_ON_ONCE(workqueue_freezing);
         workqueue_freezing = true;
 
         list_for_each_entry(wq, &workqueues, list) {
                 mutex_lock(&wq->mutex);
                 wq_adjust_max_active(wq);
                 mutex_unlock(&wq->mutex);
         }
 
         mutex_unlock(&wq_pool_mutex);
 }
 
 /**
  * freeze_workqueues_busy - are freezable workqueues still busy?
  *
  * Check whether freezing is complete.  This function must be called
  * between freeze_workqueues_begin() and thaw_workqueues().
  *
  * CONTEXT:
  * Grabs and releases wq_pool_mutex.
  *
  * Return:
  * %true if some freezable workqueues are still busy.  %false if freezing
  * is complete.
  */
 bool freeze_workqueues_busy(void)
 {
         bool busy = false;
         struct workqueue_struct *wq;
         struct pool_workqueue *pwq;
 
         mutex_lock(&wq_pool_mutex);
 
         WARN_ON_ONCE(!workqueue_freezing);
 
         list_for_each_entry(wq, &workqueues, list) {
                 if (!(wq->flags & WQ_FREEZABLE))
                         continue;
                 /*
                  * nr_active is monotonically decreasing.  It's safe
                  * to peek without lock.
                  */
                 rcu_read_lock();
                 for_each_pwq(pwq, wq) {
                         WARN_ON_ONCE(pwq->nr_active < 0);
                         if (pwq->nr_active) {
                                 busy = true;
                                 rcu_read_unlock();
                                 goto out_unlock;
                         }
                 }
                 rcu_read_unlock();
         }
 out_unlock:
         mutex_unlock(&wq_pool_mutex);
         return busy;
 }
 
 /**
  * thaw_workqueues - thaw workqueues
  *
  * Thaw workqueues.  Normal queueing is restored and all collected
  * frozen works are transferred to their respective pool worklists.
  *
  * CONTEXT:
  * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
  */
 void thaw_workqueues(void)
 {
         struct workqueue_struct *wq;
 
         mutex_lock(&wq_pool_mutex);
 
         if (!workqueue_freezing)
                 goto out_unlock;
 
         workqueue_freezing = false;
 
         /* restore max_active and repopulate worklist */
         list_for_each_entry(wq, &workqueues, list) {
                 mutex_lock(&wq->mutex);
                 wq_adjust_max_active(wq);
                 mutex_unlock(&wq->mutex);
         }
 
 out_unlock:
         mutex_unlock(&wq_pool_mutex);
 }
 #endif /* CONFIG_FREEZER */
 
 static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
 {
         LIST_HEAD(ctxs);
         int ret = 0;
         struct workqueue_struct *wq;
         struct apply_wqattrs_ctx *ctx, *n;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         list_for_each_entry(wq, &workqueues, list) {
                 if (!(wq->flags & WQ_UNBOUND) || (wq->flags & __WQ_DESTROYING))
                         continue;
 
                 ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs, unbound_cpumask);
                 if (IS_ERR(ctx)) {
                         ret = PTR_ERR(ctx);
                         break;
                 }
 
                 list_add_tail(&ctx->list, &ctxs);
         }
 
         list_for_each_entry_safe(ctx, n, &ctxs, list) {
                 if (!ret)
                         apply_wqattrs_commit(ctx);
                 apply_wqattrs_cleanup(ctx);
         }
 
         if (!ret) {
                 mutex_lock(&wq_pool_attach_mutex);
                 cpumask_copy(wq_unbound_cpumask, unbound_cpumask);
                 mutex_unlock(&wq_pool_attach_mutex);
         }
         return ret;
 }
 
 /**
  * workqueue_unbound_exclude_cpumask - Exclude given CPUs from unbound cpumask
  * @exclude_cpumask: the cpumask to be excluded from wq_unbound_cpumask
  *
  * This function can be called from cpuset code to provide a set of isolated
  * CPUs that should be excluded from wq_unbound_cpumask.
  */
 int workqueue_unbound_exclude_cpumask(cpumask_var_t exclude_cpumask)
 {
         cpumask_var_t cpumask;
         int ret = 0;
 
         if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
                 return -ENOMEM;
 
         mutex_lock(&wq_pool_mutex);
 
         /*
          * If the operation fails, it will fall back to
          * wq_requested_unbound_cpumask which is initially set to
          * (HK_TYPE_WQ ∩ HK_TYPE_DOMAIN) house keeping mask and rewritten
          * by any subsequent write to workqueue/cpumask sysfs file.
          */
         if (!cpumask_andnot(cpumask, wq_requested_unbound_cpumask, exclude_cpumask))
                 cpumask_copy(cpumask, wq_requested_unbound_cpumask);
         if (!cpumask_equal(cpumask, wq_unbound_cpumask))
                 ret = workqueue_apply_unbound_cpumask(cpumask);
 
         /* Save the current isolated cpumask & export it via sysfs */
         if (!ret)
                 cpumask_copy(wq_isolated_cpumask, exclude_cpumask);
 
         mutex_unlock(&wq_pool_mutex);
         free_cpumask_var(cpumask);
         return ret;
 }
 
 static int parse_affn_scope(const char *val)
 {
         int i;
 
         for (i = 0; i < ARRAY_SIZE(wq_affn_names); i++) {
                 if (!strncasecmp(val, wq_affn_names[i], strlen(wq_affn_names[i])))
                         return i;
         }
         return -EINVAL;
 }
 
 static int wq_affn_dfl_set(const char *val, const struct kernel_param *kp)
 {
         struct workqueue_struct *wq;
         int affn, cpu;
 
         affn = parse_affn_scope(val);
         if (affn < 0)
                 return affn;
         if (affn == WQ_AFFN_DFL)
                 return -EINVAL;
 
         cpus_read_lock();
         mutex_lock(&wq_pool_mutex);
 
         wq_affn_dfl = affn;
 
         list_for_each_entry(wq, &workqueues, list) {
                 for_each_online_cpu(cpu)
                         unbound_wq_update_pwq(wq, cpu);
         }
 
         mutex_unlock(&wq_pool_mutex);
         cpus_read_unlock();
 
         return 0;
 }
 
 static int wq_affn_dfl_get(char *buffer, const struct kernel_param *kp)
 {
         return scnprintf(buffer, PAGE_SIZE, "%s\n", wq_affn_names[wq_affn_dfl]);
 }
 
 static const struct kernel_param_ops wq_affn_dfl_ops = {
         .set    = wq_affn_dfl_set,
         .get    = wq_affn_dfl_get,
 };
 
 module_param_cb(default_affinity_scope, &wq_affn_dfl_ops, NULL, 0644);
 
 #ifdef CONFIG_SYSFS
 /*
  * Workqueues with WQ_SYSFS flag set is visible to userland via
  * /sys/bus/workqueue/devices/WQ_NAME.  All visible workqueues have the
  * following attributes.
  *
  *  per_cpu             RO bool : whether the workqueue is per-cpu or unbound
  *  max_active          RW int  : maximum number of in-flight work items
  *
  * Unbound workqueues have the following extra attributes.
  *
  *  nice                RW int  : nice value of the workers
  *  cpumask             RW mask : bitmask of allowed CPUs for the workers
  *  affinity_scope      RW str  : worker CPU affinity scope (cache, numa, none)
  *  affinity_strict     RW bool : worker CPU affinity is strict
  */
 struct wq_device {
         struct workqueue_struct         *wq;
         struct device                   dev;
 };
 
 static struct workqueue_struct *dev_to_wq(struct device *dev)
 {
         struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
 
         return wq_dev->wq;
 }
 
 static ssize_t per_cpu_show(struct device *dev, struct device_attribute *attr,
                             char *buf)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
 
         return scnprintf(buf, PAGE_SIZE, "%d\n", (bool)!(wq->flags & WQ_UNBOUND));
 }
 static DEVICE_ATTR_RO(per_cpu);
 
 static ssize_t max_active_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
 
         return scnprintf(buf, PAGE_SIZE, "%d\n", wq->saved_max_active);
 }
 
 static ssize_t max_active_store(struct device *dev,
                                 struct device_attribute *attr, const char *buf,
                                 size_t count)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         int val;
 
         if (sscanf(buf, "%d", &val) != 1 || val <= 0)
                 return -EINVAL;
 
         workqueue_set_max_active(wq, val);
         return count;
 }
 static DEVICE_ATTR_RW(max_active);
 
 static struct attribute *wq_sysfs_attrs[] = {
         &dev_attr_per_cpu.attr,
         &dev_attr_max_active.attr,
         NULL,
 };
 ATTRIBUTE_GROUPS(wq_sysfs);
 
 static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
                             char *buf)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         int written;
 
         mutex_lock(&wq->mutex);
         written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->unbound_attrs->nice);
         mutex_unlock(&wq->mutex);
 
         return written;
 }
 
 /* prepare workqueue_attrs for sysfs store operations */
 static struct workqueue_attrs *wq_sysfs_prep_attrs(struct workqueue_struct *wq)
 {
         struct workqueue_attrs *attrs;
 
         lockdep_assert_held(&wq_pool_mutex);
 
         attrs = alloc_workqueue_attrs();
         if (!attrs)
                 return NULL;
 
         copy_workqueue_attrs(attrs, wq->unbound_attrs);
         return attrs;
 }
 
 static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
                              const char *buf, size_t count)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         struct workqueue_attrs *attrs;
         int ret = -ENOMEM;
 
         apply_wqattrs_lock();
 
         attrs = wq_sysfs_prep_attrs(wq);
         if (!attrs)
                 goto out_unlock;
 
         if (sscanf(buf, "%d", &attrs->nice) == 1 &&
             attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
                 ret = apply_workqueue_attrs_locked(wq, attrs);
         else
                 ret = -EINVAL;
 
 out_unlock:
         apply_wqattrs_unlock();
         free_workqueue_attrs(attrs);
         return ret ?: count;
 }
 
 static ssize_t wq_cpumask_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         int written;
 
         mutex_lock(&wq->mutex);
         written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
                             cpumask_pr_args(wq->unbound_attrs->cpumask));
         mutex_unlock(&wq->mutex);
         return written;
 }
 
 static ssize_t wq_cpumask_store(struct device *dev,
                                 struct device_attribute *attr,
                                 const char *buf, size_t count)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         struct workqueue_attrs *attrs;
         int ret = -ENOMEM;
 
         apply_wqattrs_lock();
 
         attrs = wq_sysfs_prep_attrs(wq);
         if (!attrs)
                 goto out_unlock;
 
         ret = cpumask_parse(buf, attrs->cpumask);
         if (!ret)
                 ret = apply_workqueue_attrs_locked(wq, attrs);
 
 out_unlock:
         apply_wqattrs_unlock();
         free_workqueue_attrs(attrs);
         return ret ?: count;
 }
 
 static ssize_t wq_affn_scope_show(struct device *dev,
                                   struct device_attribute *attr, char *buf)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         int written;
 
         mutex_lock(&wq->mutex);
         if (wq->unbound_attrs->affn_scope == WQ_AFFN_DFL)
                 written = scnprintf(buf, PAGE_SIZE, "%s (%s)\n",
                                     wq_affn_names[WQ_AFFN_DFL],
                                     wq_affn_names[wq_affn_dfl]);
         else
                 written = scnprintf(buf, PAGE_SIZE, "%s\n",
                                     wq_affn_names[wq->unbound_attrs->affn_scope]);
         mutex_unlock(&wq->mutex);
 
         return written;
 }
 
 static ssize_t wq_affn_scope_store(struct device *dev,
                                    struct device_attribute *attr,
                                    const char *buf, size_t count)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         struct workqueue_attrs *attrs;
         int affn, ret = -ENOMEM;
 
         affn = parse_affn_scope(buf);
         if (affn < 0)
                 return affn;
 
         apply_wqattrs_lock();
         attrs = wq_sysfs_prep_attrs(wq);
         if (attrs) {
                 attrs->affn_scope = affn;
                 ret = apply_workqueue_attrs_locked(wq, attrs);
         }
         apply_wqattrs_unlock();
         free_workqueue_attrs(attrs);
         return ret ?: count;
 }
 
 static ssize_t wq_affinity_strict_show(struct device *dev,
                                        struct device_attribute *attr, char *buf)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
 
         return scnprintf(buf, PAGE_SIZE, "%d\n",
                          wq->unbound_attrs->affn_strict);
 }
 
 static ssize_t wq_affinity_strict_store(struct device *dev,
                                         struct device_attribute *attr,
                                         const char *buf, size_t count)
 {
         struct workqueue_struct *wq = dev_to_wq(dev);
         struct workqueue_attrs *attrs;
         int v, ret = -ENOMEM;
 
         if (sscanf(buf, "%d", &v) != 1)
                 return -EINVAL;
 
         apply_wqattrs_lock();
         attrs = wq_sysfs_prep_attrs(wq);
         if (attrs) {
                 attrs->affn_strict = (bool)v;
                 ret = apply_workqueue_attrs_locked(wq, attrs);
         }
         apply_wqattrs_unlock();
         free_workqueue_attrs(attrs);
         return ret ?: count;
 }
 
 static struct device_attribute wq_sysfs_unbound_attrs[] = {
         __ATTR(nice, 0644, wq_nice_show, wq_nice_store),
         __ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store),
         __ATTR(affinity_scope, 0644, wq_affn_scope_show, wq_affn_scope_store),
         __ATTR(affinity_strict, 0644, wq_affinity_strict_show, wq_affinity_strict_store),
         __ATTR_NULL,
 };
 
 static const struct bus_type wq_subsys = {
         .name                           = "workqueue",
         .dev_groups                     = wq_sysfs_groups,
 };
 
 /**
  *  workqueue_set_unbound_cpumask - Set the low-level unbound cpumask
  *  @cpumask: the cpumask to set
  *
  *  The low-level workqueues cpumask is a global cpumask that limits
  *  the affinity of all unbound workqueues.  This function check the @cpumask
  *  and apply it to all unbound workqueues and updates all pwqs of them.
  *
  *  Return:     0       - Success
  *              -EINVAL - Invalid @cpumask
  *              -ENOMEM - Failed to allocate memory for attrs or pwqs.
  */
 static int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 {
         int ret = -EINVAL;
 
         /*
          * Not excluding isolated cpus on purpose.
          * If the user wishes to include them, we allow that.
          */
         cpumask_and(cpumask, cpumask, cpu_possible_mask);
         if (!cpumask_empty(cpumask)) {
                 ret = 0;
                 apply_wqattrs_lock();
                 if (!cpumask_equal(cpumask, wq_unbound_cpumask))
                         ret = workqueue_apply_unbound_cpumask(cpumask);
                 if (!ret)
                         cpumask_copy(wq_requested_unbound_cpumask, cpumask);
                 apply_wqattrs_unlock();
         }
 
         return ret;
 }
 
 static ssize_t __wq_cpumask_show(struct device *dev,
                 struct device_attribute *attr, char *buf, cpumask_var_t mask)
 {
         int written;
 
         mutex_lock(&wq_pool_mutex);
         written = scnprintf(buf, PAGE_SIZE, "%*pb\n", cpumask_pr_args(mask));
         mutex_unlock(&wq_pool_mutex);
 
         return written;
 }
 
 static ssize_t cpumask_requested_show(struct device *dev,
                 struct device_attribute *attr, char *buf)
 {
         return __wq_cpumask_show(dev, attr, buf, wq_requested_unbound_cpumask);
 }
 static DEVICE_ATTR_RO(cpumask_requested);
 
 static ssize_t cpumask_isolated_show(struct device *dev,
                 struct device_attribute *attr, char *buf)
 {
         return __wq_cpumask_show(dev, attr, buf, wq_isolated_cpumask);
 }
 static DEVICE_ATTR_RO(cpumask_isolated);
 
 static ssize_t cpumask_show(struct device *dev,
                 struct device_attribute *attr, char *buf)
 {
         return __wq_cpumask_show(dev, attr, buf, wq_unbound_cpumask);
 }
 
 static ssize_t cpumask_store(struct device *dev,
                 struct device_attribute *attr, const char *buf, size_t count)
 {
         cpumask_var_t cpumask;
         int ret;
 
         if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
                 return -ENOMEM;
 
         ret = cpumask_parse(buf, cpumask);
         if (!ret)
                 ret = workqueue_set_unbound_cpumask(cpumask);
 
         free_cpumask_var(cpumask);
         return ret ? ret : count;
 }
 static DEVICE_ATTR_RW(cpumask);
 
 static struct attribute *wq_sysfs_cpumask_attrs[] = {
         &dev_attr_cpumask.attr,
         &dev_attr_cpumask_requested.attr,
         &dev_attr_cpumask_isolated.attr,
         NULL,
 };
 ATTRIBUTE_GROUPS(wq_sysfs_cpumask);
 
 static int __init wq_sysfs_init(void)
 {
         return subsys_virtual_register(&wq_subsys, wq_sysfs_cpumask_groups);
 }
 core_initcall(wq_sysfs_init);
 
 static void wq_device_release(struct device *dev)
 {
         struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);
 
         kfree(wq_dev);
 }
 
 /**
  * workqueue_sysfs_register - make a workqueue visible in sysfs
  * @wq: the workqueue to register
  *
  * Expose @wq in sysfs under /sys/bus/workqueue/devices.
  * alloc_workqueue*() automatically calls this function if WQ_SYSFS is set
  * which is the preferred method.
  *
  * Workqueue user should use this function directly iff it wants to apply
  * workqueue_attrs before making the workqueue visible in sysfs; otherwise,
  * apply_workqueue_attrs() may race against userland updating the
  * attributes.
  *
  * Return: 0 on success, -errno on failure.
  */
 int workqueue_sysfs_register(struct workqueue_struct *wq)
 {
         struct wq_device *wq_dev;
         int ret;
 
         /*
          * Adjusting max_active breaks ordering guarantee.  Disallow exposing
          * ordered workqueues.
          */
         if (WARN_ON(wq->flags & __WQ_ORDERED))
                 return -EINVAL;
 
         wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);
         if (!wq_dev)
                 return -ENOMEM;
 
         wq_dev->wq = wq;
         wq_dev->dev.bus = &wq_subsys;
         wq_dev->dev.release = wq_device_release;
         dev_set_name(&wq_dev->dev, "%s", wq->name);
 
         /*
          * unbound_attrs are created separately.  Suppress uevent until
          * everything is ready.
          */
         dev_set_uevent_suppress(&wq_dev->dev, true);
 
         ret = device_register(&wq_dev->dev);
         if (ret) {
                 put_device(&wq_dev->dev);
                 wq->wq_dev = NULL;
                 return ret;
         }
 
         if (wq->flags & WQ_UNBOUND) {
                 struct device_attribute *attr;
 
                 for (attr = wq_sysfs_unbound_attrs; attr->attr.name; attr++) {
                         ret = device_create_file(&wq_dev->dev, attr);
                         if (ret) {
                                 device_unregister(&wq_dev->dev);
                                 wq->wq_dev = NULL;
                                 return ret;
                         }
                 }
         }
 
         dev_set_uevent_suppress(&wq_dev->dev, false);
         kobject_uevent(&wq_dev->dev.kobj, KOBJ_ADD);
         return 0;
 }
 
 /**
  * workqueue_sysfs_unregister - undo workqueue_sysfs_register()
  * @wq: the workqueue to unregister
  *
  * If @wq is registered to sysfs by workqueue_sysfs_register(), unregister.
  */
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
 {
         struct wq_device *wq_dev = wq->wq_dev;
 
         if (!wq->wq_dev)
                 return;
 
         wq->wq_dev = NULL;
         device_unregister(&wq_dev->dev);
 }
 #else   /* CONFIG_SYSFS */
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq)     { }
 #endif  /* CONFIG_SYSFS */
 
 /*
  * Workqueue watchdog.
  *
  * Stall may be caused by various bugs - missing WQ_MEM_RECLAIM, illegal
  * flush dependency, a concurrency managed work item which stays RUNNING
  * indefinitely.  Workqueue stalls can be very difficult to debug as the
  * usual warning mechanisms don't trigger and internal workqueue state is
  * largely opaque.
  *
  * Workqueue watchdog monitors all worker pools periodically and dumps
  * state if some pools failed to make forward progress for a while where
  * forward progress is defined as the first item on ->worklist changing.
  *
  * This mechanism is controlled through the kernel parameter
  * "workqueue.watchdog_thresh" which can be updated at runtime through the
  * corresponding sysfs parameter file.
  */
 #ifdef CONFIG_WQ_WATCHDOG
 
 static unsigned long wq_watchdog_thresh = 30;
 static struct timer_list wq_watchdog_timer;
 
 static unsigned long wq_watchdog_touched = INITIAL_JIFFIES;
 static DEFINE_PER_CPU(unsigned long, wq_watchdog_touched_cpu) = INITIAL_JIFFIES;
 
 /*
  * Show workers that might prevent the processing of pending work items.
  * The only candidates are CPU-bound workers in the running state.
  * Pending work items should be handled by another idle worker
  * in all other situations.
  */
 static void show_cpu_pool_hog(struct worker_pool *pool)
 {
         struct worker *worker;
         unsigned long irq_flags;
         int bkt;
 
         raw_spin_lock_irqsave(&pool->lock, irq_flags);
 
         hash_for_each(pool->busy_hash, bkt, worker, hentry) {
                 if (task_is_running(worker->task)) {
                         /*
                          * Defer printing to avoid deadlocks in console
                          * drivers that queue work while holding locks
                          * also taken in their write paths.
                          */
                         printk_deferred_enter();
 
                         pr_info("pool %d:\n", pool->id);
                         sched_show_task(worker->task);
 
                         printk_deferred_exit();
                 }
         }
 
         raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
 }
 
 static void show_cpu_pools_hogs(void)
 {
         struct worker_pool *pool;
         int pi;
 
         pr_info("Showing backtraces of running workers in stalled CPU-bound worker pools:\n");
 
         rcu_read_lock();
 
         for_each_pool(pool, pi) {
                 if (pool->cpu_stall)
                         show_cpu_pool_hog(pool);
 
         }
 
         rcu_read_unlock();
 }
 
 static void wq_watchdog_reset_touched(void)
 {
         int cpu;
 
         wq_watchdog_touched = jiffies;
         for_each_possible_cpu(cpu)
                 per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
 }
 
 static void wq_watchdog_timer_fn(struct timer_list *unused)
 {
         unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
         bool lockup_detected = false;
         bool cpu_pool_stall = false;
         unsigned long now = jiffies;
         struct worker_pool *pool;
         int pi;
 
         if (!thresh)
                 return;
 
         rcu_read_lock();
 
         for_each_pool(pool, pi) {
                 unsigned long pool_ts, touched, ts;
 
                 pool->cpu_stall = false;
                 if (list_empty(&pool->worklist))
                         continue;
 
                 /*
                  * If a virtual machine is stopped by the host it can look to
                  * the watchdog like a stall.
                  */
                 kvm_check_and_clear_guest_paused();
 
                 /* get the latest of pool and touched timestamps */
                 if (pool->cpu >= 0)
                         touched = READ_ONCE(per_cpu(wq_watchdog_touched_cpu, pool->cpu));
                 else
                         touched = READ_ONCE(wq_watchdog_touched);
                 pool_ts = READ_ONCE(pool->watchdog_ts);
 
                 if (time_after(pool_ts, touched))
                         ts = pool_ts;
                 else
                         ts = touched;
 
                 /* did we stall? */
                 if (time_after(now, ts + thresh)) {
                         lockup_detected = true;
                         if (pool->cpu >= 0 && !(pool->flags & POOL_BH)) {
                                 pool->cpu_stall = true;
                                 cpu_pool_stall = true;
                         }
                         pr_emerg("BUG: workqueue lockup - pool");
                         pr_cont_pool_info(pool);
                         pr_cont(" stuck for %us!\n",
                                 jiffies_to_msecs(now - pool_ts) / 1000);
                 }
 
 
         }
 
         rcu_read_unlock();
 
         if (lockup_detected)
                 show_all_workqueues();
 
         if (cpu_pool_stall)
                 show_cpu_pools_hogs();
 
         wq_watchdog_reset_touched();
         mod_timer(&wq_watchdog_timer, jiffies + thresh);
 }
 
 notrace void wq_watchdog_touch(int cpu)
 {
         unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
         unsigned long touch_ts = READ_ONCE(wq_watchdog_touched);
         unsigned long now = jiffies;
 
         if (cpu >= 0)
                 per_cpu(wq_watchdog_touched_cpu, cpu) = now;
         else
                 WARN_ONCE(1, "%s should be called with valid CPU", __func__);
 
         /* Don't unnecessarily store to global cacheline */
         if (time_after(now, touch_ts + thresh / 4))
                 WRITE_ONCE(wq_watchdog_touched, jiffies);
 }
 
 static void wq_watchdog_set_thresh(unsigned long thresh)
 {
         wq_watchdog_thresh = 0;
         del_timer_sync(&wq_watchdog_timer);
 
         if (thresh) {
                 wq_watchdog_thresh = thresh;
                 wq_watchdog_reset_touched();
                 mod_timer(&wq_watchdog_timer, jiffies + thresh * HZ);
         }
 }
 
 static int wq_watchdog_param_set_thresh(const char *val,
                                         const struct kernel_param *kp)
 {
         unsigned long thresh;
         int ret;
 
         ret = kstrtoul(val, 0, &thresh);
         if (ret)
                 return ret;
 
         if (system_wq)
                 wq_watchdog_set_thresh(thresh);
         else
                 wq_watchdog_thresh = thresh;
 
         return 0;
 }
 
 static const struct kernel_param_ops wq_watchdog_thresh_ops = {
         .set    = wq_watchdog_param_set_thresh,
         .get    = param_get_ulong,
 };
 
 module_param_cb(watchdog_thresh, &wq_watchdog_thresh_ops, &wq_watchdog_thresh,
                 0644);
 
 static void wq_watchdog_init(void)
 {
         timer_setup(&wq_watchdog_timer, wq_watchdog_timer_fn, TIMER_DEFERRABLE);
         wq_watchdog_set_thresh(wq_watchdog_thresh);
 }
 
 #else   /* CONFIG_WQ_WATCHDOG */
 
 static inline void wq_watchdog_init(void) { }
 
 #endif  /* CONFIG_WQ_WATCHDOG */
 
 static void bh_pool_kick_normal(struct irq_work *irq_work)
 {
         raise_softirq_irqoff(TASKLET_SOFTIRQ);
 }
 
 static void bh_pool_kick_highpri(struct irq_work *irq_work)
 {
         raise_softirq_irqoff(HI_SOFTIRQ);
 }
 
 static void __init restrict_unbound_cpumask(const char *name, const struct cpumask *mask)
 {
         if (!cpumask_intersects(wq_unbound_cpumask, mask)) {
                 pr_warn("workqueue: Restricting unbound_cpumask (%*pb) with %s (%*pb) leaves no CPU, ignoring\n",
                         cpumask_pr_args(wq_unbound_cpumask), name, cpumask_pr_args(mask));
                 return;
         }
 
         cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, mask);
 }
 
 static void __init init_cpu_worker_pool(struct worker_pool *pool, int cpu, int nice)
 {
         BUG_ON(init_worker_pool(pool));
         pool->cpu = cpu;
         cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
         cpumask_copy(pool->attrs->__pod_cpumask, cpumask_of(cpu));
         pool->attrs->nice = nice;
         pool->attrs->affn_strict = true;
         pool->node = cpu_to_node(cpu);
 
         /* alloc pool ID */
         mutex_lock(&wq_pool_mutex);
         BUG_ON(worker_pool_assign_id(pool));
         mutex_unlock(&wq_pool_mutex);
 }
 
 /**
  * workqueue_init_early - early init for workqueue subsystem
  *
  * This is the first step of three-staged workqueue subsystem initialization and
  * invoked as soon as the bare basics - memory allocation, cpumasks and idr are
  * up. It sets up all the data structures and system workqueues and allows early
  * boot code to create workqueues and queue/cancel work items. Actual work item
  * execution starts only after kthreads can be created and scheduled right
  * before early initcalls.
  */
 void __init workqueue_init_early(void)
 {
         struct wq_pod_type *pt = &wq_pod_types[WQ_AFFN_SYSTEM];
         int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
         void (*irq_work_fns[2])(struct irq_work *) = { bh_pool_kick_normal,
                                                        bh_pool_kick_highpri };
         int i, cpu;
 
         BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
 
         BUG_ON(!alloc_cpumask_var(&wq_online_cpumask, GFP_KERNEL));
         BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
         BUG_ON(!alloc_cpumask_var(&wq_requested_unbound_cpumask, GFP_KERNEL));
         BUG_ON(!zalloc_cpumask_var(&wq_isolated_cpumask, GFP_KERNEL));
 
         cpumask_copy(wq_online_cpumask, cpu_online_mask);
         cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);
         restrict_unbound_cpumask("HK_TYPE_WQ", housekeeping_cpumask(HK_TYPE_WQ));
         restrict_unbound_cpumask("HK_TYPE_DOMAIN", housekeeping_cpumask(HK_TYPE_DOMAIN));
         if (!cpumask_empty(&wq_cmdline_cpumask))
                 restrict_unbound_cpumask("workqueue.unbound_cpus", &wq_cmdline_cpumask);
 
         cpumask_copy(wq_requested_unbound_cpumask, wq_unbound_cpumask);
 
         pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);
 
         unbound_wq_update_pwq_attrs_buf = alloc_workqueue_attrs();
         BUG_ON(!unbound_wq_update_pwq_attrs_buf);
 
         /*
          * If nohz_full is enabled, set power efficient workqueue as unbound.
          * This allows workqueue items to be moved to HK CPUs.
          */
         if (housekeeping_enabled(HK_TYPE_TICK))
                 wq_power_efficient = true;
 
         /* initialize WQ_AFFN_SYSTEM pods */
         pt->pod_cpus = kcalloc(1, sizeof(pt->pod_cpus[0]), GFP_KERNEL);
         pt->pod_node = kcalloc(1, sizeof(pt->pod_node[0]), GFP_KERNEL);
         pt->cpu_pod = kcalloc(nr_cpu_ids, sizeof(pt->cpu_pod[0]), GFP_KERNEL);
         BUG_ON(!pt->pod_cpus || !pt->pod_node || !pt->cpu_pod);
 
         BUG_ON(!zalloc_cpumask_var_node(&pt->pod_cpus[0], GFP_KERNEL, NUMA_NO_NODE));
 
         pt->nr_pods = 1;
         cpumask_copy(pt->pod_cpus[0], cpu_possible_mask);
         pt->pod_node[0] = NUMA_NO_NODE;
         pt->cpu_pod[0] = 0;
 
         /* initialize BH and CPU pools */
         for_each_possible_cpu(cpu) {
                 struct worker_pool *pool;
 
                 i = 0;
                 for_each_bh_worker_pool(pool, cpu) {
                         init_cpu_worker_pool(pool, cpu, std_nice[i]);
                         pool->flags |= POOL_BH;
                         init_irq_work(bh_pool_irq_work(pool), irq_work_fns[i]);
                         i++;
                 }
 
                 i = 0;
                 for_each_cpu_worker_pool(pool, cpu)
                         init_cpu_worker_pool(pool, cpu, std_nice[i++]);
         }
 
         /* create default unbound and ordered wq attrs */
         for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
                 struct workqueue_attrs *attrs;
 
                 BUG_ON(!(attrs = alloc_workqueue_attrs()));
                 attrs->nice = std_nice[i];
                 unbound_std_wq_attrs[i] = attrs;
 
                 /*
                  * An ordered wq should have only one pwq as ordering is
                  * guaranteed by max_active which is enforced by pwqs.
                  */
                 BUG_ON(!(attrs = alloc_workqueue_attrs()));
                 attrs->nice = std_nice[i];
                 attrs->ordered = true;
                 ordered_wq_attrs[i] = attrs;
         }
 
         system_wq = alloc_workqueue("events", 0, 0);
         system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
         system_long_wq = alloc_workqueue("events_long", 0, 0);
         system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
                                             WQ_MAX_ACTIVE);
         system_freezable_wq = alloc_workqueue("events_freezable",
                                               WQ_FREEZABLE, 0);
         system_power_efficient_wq = alloc_workqueue("events_power_efficient",
                                               WQ_POWER_EFFICIENT, 0);
         system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_pwr_efficient",
                                               WQ_FREEZABLE | WQ_POWER_EFFICIENT,
                                               0);
         system_bh_wq = alloc_workqueue("events_bh", WQ_BH, 0);
         system_bh_highpri_wq = alloc_workqueue("events_bh_highpri",
                                                WQ_BH | WQ_HIGHPRI, 0);
         BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
                !system_unbound_wq || !system_freezable_wq ||
                !system_power_efficient_wq ||
                !system_freezable_power_efficient_wq ||
                !system_bh_wq || !system_bh_highpri_wq);
 }
 
 static void __init wq_cpu_intensive_thresh_init(void)
 {
         unsigned long thresh;
         unsigned long bogo;
 
         pwq_release_worker = kthread_create_worker(0, "pool_workqueue_release");
         BUG_ON(IS_ERR(pwq_release_worker));
 
         /* if the user set it to a specific value, keep it */
         if (wq_cpu_intensive_thresh_us != ULONG_MAX)
                 return;
 
         /*
          * The default of 10ms is derived from the fact that most modern (as of
          * 2023) processors can do a lot in 10ms and that it's just below what
          * most consider human-perceivable. However, the kernel also runs on a
          * lot slower CPUs including microcontrollers where the threshold is way
          * too low.
          *
          * Let's scale up the threshold upto 1 second if BogoMips is below 4000.
          * This is by no means accurate but it doesn't have to be. The mechanism
          * is still useful even when the threshold is fully scaled up. Also, as
          * the reports would usually be applicable to everyone, some machines
          * operating on longer thresholds won't significantly diminish their
          * usefulness.
          */
         thresh = 10 * USEC_PER_MSEC;
 
         /* see init/calibrate.c for lpj -> BogoMIPS calculation */
         bogo = max_t(unsigned long, loops_per_jiffy / 500000 * HZ, 1);
         if (bogo < 4000)
                 thresh = min_t(unsigned long, thresh * 4000 / bogo, USEC_PER_SEC);
 
         pr_debug("wq_cpu_intensive_thresh: lpj=%lu BogoMIPS=%lu thresh_us=%lu\n",
                  loops_per_jiffy, bogo, thresh);
 
         wq_cpu_intensive_thresh_us = thresh;
 }
 
 /**
  * workqueue_init - bring workqueue subsystem fully online
  *
  * This is the second step of three-staged workqueue subsystem initialization
  * and invoked as soon as kthreads can be created and scheduled. Workqueues have
  * been created and work items queued on them, but there are no kworkers
  * executing the work items yet. Populate the worker pools with the initial
  * workers and enable future kworker creations.
  */
 void __init workqueue_init(void)
 {
         struct workqueue_struct *wq;
         struct worker_pool *pool;
         int cpu, bkt;
 
         wq_cpu_intensive_thresh_init();
 
         mutex_lock(&wq_pool_mutex);
 
         /*
          * Per-cpu pools created earlier could be missing node hint. Fix them
          * up. Also, create a rescuer for workqueues that requested it.
          */
         for_each_possible_cpu(cpu) {
                 for_each_bh_worker_pool(pool, cpu)
                         pool->node = cpu_to_node(cpu);
                 for_each_cpu_worker_pool(pool, cpu)
                         pool->node = cpu_to_node(cpu);
         }
 
         list_for_each_entry(wq, &workqueues, list) {
                 WARN(init_rescuer(wq),
                      "workqueue: failed to create early rescuer for %s",
                      wq->name);
         }
 
         mutex_unlock(&wq_pool_mutex);
 
         /*
          * Create the initial workers. A BH pool has one pseudo worker that
          * represents the shared BH execution context and thus doesn't get
          * affected by hotplug events. Create the BH pseudo workers for all
          * possible CPUs here.
          */
         for_each_possible_cpu(cpu)
                 for_each_bh_worker_pool(pool, cpu)
                         BUG_ON(!create_worker(pool));
 
         for_each_online_cpu(cpu) {
                 for_each_cpu_worker_pool(pool, cpu) {
                         pool->flags &= ~POOL_DISASSOCIATED;
                         BUG_ON(!create_worker(pool));
                 }
         }
 
         hash_for_each(unbound_pool_hash, bkt, pool, hash_node)
                 BUG_ON(!create_worker(pool));
 
         wq_online = true;
         wq_watchdog_init();
 }
 
 /*
  * Initialize @pt by first initializing @pt->cpu_pod[] with pod IDs according to
  * @cpu_shares_pod(). Each subset of CPUs that share a pod is assigned a unique
  * and consecutive pod ID. The rest of @pt is initialized accordingly.
  */
 static void __init init_pod_type(struct wq_pod_type *pt,
                                  bool (*cpus_share_pod)(int, int))
 {
         int cur, pre, cpu, pod;
 
         pt->nr_pods = 0;
 
         /* init @pt->cpu_pod[] according to @cpus_share_pod() */
         pt->cpu_pod = kcalloc(nr_cpu_ids, sizeof(pt->cpu_pod[0]), GFP_KERNEL);
         BUG_ON(!pt->cpu_pod);
 
         for_each_possible_cpu(cur) {
                 for_each_possible_cpu(pre) {
                         if (pre >= cur) {
                                 pt->cpu_pod[cur] = pt->nr_pods++;
                                 break;
                         }
                         if (cpus_share_pod(cur, pre)) {
                                 pt->cpu_pod[cur] = pt->cpu_pod[pre];
                                 break;
                         }
                 }
         }
 
         /* init the rest to match @pt->cpu_pod[] */
         pt->pod_cpus = kcalloc(pt->nr_pods, sizeof(pt->pod_cpus[0]), GFP_KERNEL);
         pt->pod_node = kcalloc(pt->nr_pods, sizeof(pt->pod_node[0]), GFP_KERNEL);
         BUG_ON(!pt->pod_cpus || !pt->pod_node);
 
         for (pod = 0; pod < pt->nr_pods; pod++)
                 BUG_ON(!zalloc_cpumask_var(&pt->pod_cpus[pod], GFP_KERNEL));
 
         for_each_possible_cpu(cpu) {
                 cpumask_set_cpu(cpu, pt->pod_cpus[pt->cpu_pod[cpu]]);
                 pt->pod_node[pt->cpu_pod[cpu]] = cpu_to_node(cpu);
         }
 }
 
 static bool __init cpus_dont_share(int cpu0, int cpu1)
 {
         return false;
 }
 
 static bool __init cpus_share_smt(int cpu0, int cpu1)
 {
 #ifdef CONFIG_SCHED_SMT
         return cpumask_test_cpu(cpu0, cpu_smt_mask(cpu1));
 #else
         return false;
 #endif
 }
 
 static bool __init cpus_share_numa(int cpu0, int cpu1)
 {
         return cpu_to_node(cpu0) == cpu_to_node(cpu1);
 }
 
 /**
  * workqueue_init_topology - initialize CPU pods for unbound workqueues
  *
  * This is the third step of three-staged workqueue subsystem initialization and
  * invoked after SMP and topology information are fully initialized. It
  * initializes the unbound CPU pods accordingly.
  */
 void __init workqueue_init_topology(void)
 {
         struct workqueue_struct *wq;
         int cpu;
 
         init_pod_type(&wq_pod_types[WQ_AFFN_CPU], cpus_dont_share);
         init_pod_type(&wq_pod_types[WQ_AFFN_SMT], cpus_share_smt);
         init_pod_type(&wq_pod_types[WQ_AFFN_CACHE], cpus_share_cache);
         init_pod_type(&wq_pod_types[WQ_AFFN_NUMA], cpus_share_numa);
 
         wq_topo_initialized = true;
 
         mutex_lock(&wq_pool_mutex);
 
         /*
          * Workqueues allocated earlier would have all CPUs sharing the default
          * worker pool. Explicitly call unbound_wq_update_pwq() on all workqueue
          * and CPU combinations to apply per-pod sharing.
          */
         list_for_each_entry(wq, &workqueues, list) {
                 for_each_online_cpu(cpu)
                         unbound_wq_update_pwq(wq, cpu);
                 if (wq->flags & WQ_UNBOUND) {
                         mutex_lock(&wq->mutex);
                         wq_update_node_max_active(wq, -1);
                         mutex_unlock(&wq->mutex);
                 }
         }
 
         mutex_unlock(&wq_pool_mutex);
 }
 
 void __warn_flushing_systemwide_wq(void)
 {
         pr_warn("WARNING: Flushing system-wide workqueues will be prohibited in near future.\n");
         dump_stack();
 }
 EXPORT_SYMBOL(__warn_flushing_systemwide_wq);
 
 static int __init workqueue_unbound_cpus_setup(char *str)
 {
         if (cpulist_parse(str, &wq_cmdline_cpumask) < 0) {
                 cpumask_clear(&wq_cmdline_cpumask);
                 pr_warn("workqueue.unbound_cpus: incorrect CPU range, using default\n");
         }
 
         return 1;
 }
 __setup("workqueue.unbound_cpus=", workqueue_unbound_cpus_setup);