TOMOYO Linux Cross Reference
Linux/kernel/cpu.c

   /* CPU control.
    * (C) 2001, 2002, 2003, 2004 Rusty Russell
    *
    * This code is licenced under the GPL.
    */
   #include <linux/sched/mm.h>
   #include <linux/proc_fs.h>
   #include <linux/smp.h>
   #include <linux/init.h>
  #include <linux/notifier.h>
  #include <linux/sched/signal.h>
  #include <linux/sched/hotplug.h>
  #include <linux/sched/isolation.h>
  #include <linux/sched/task.h>
  #include <linux/sched/smt.h>
  #include <linux/unistd.h>
  #include <linux/cpu.h>
  #include <linux/oom.h>
  #include <linux/rcupdate.h>
  #include <linux/delay.h>
  #include <linux/export.h>
  #include <linux/bug.h>
  #include <linux/kthread.h>
  #include <linux/stop_machine.h>
  #include <linux/mutex.h>
  #include <linux/gfp.h>
  #include <linux/suspend.h>
  #include <linux/lockdep.h>
  #include <linux/tick.h>
  #include <linux/irq.h>
  #include <linux/nmi.h>
  #include <linux/smpboot.h>
  #include <linux/relay.h>
  #include <linux/slab.h>
  #include <linux/scs.h>
  #include <linux/percpu-rwsem.h>
  #include <linux/cpuset.h>
  #include <linux/random.h>
  #include <linux/cc_platform.h>
  
  #include <trace/events/power.h>
  #define CREATE_TRACE_POINTS
  #include <trace/events/cpuhp.h>
  
  #include "smpboot.h"
  
  /**
   * struct cpuhp_cpu_state - Per cpu hotplug state storage
   * @state:      The current cpu state
   * @target:     The target state
   * @fail:       Current CPU hotplug callback state
   * @thread:     Pointer to the hotplug thread
   * @should_run: Thread should execute
   * @rollback:   Perform a rollback
   * @single:     Single callback invocation
   * @bringup:    Single callback bringup or teardown selector
   * @node:       Remote CPU node; for multi-instance, do a
   *              single entry callback for install/remove
   * @last:       For multi-instance rollback, remember how far we got
   * @cb_state:   The state for a single callback (install/uninstall)
   * @result:     Result of the operation
   * @ap_sync_state:      State for AP synchronization
   * @done_up:    Signal completion to the issuer of the task for cpu-up
   * @done_down:  Signal completion to the issuer of the task for cpu-down
   */
  struct cpuhp_cpu_state {
          enum cpuhp_state        state;
          enum cpuhp_state        target;
          enum cpuhp_state        fail;
  #ifdef CONFIG_SMP
          struct task_struct      *thread;
          bool                    should_run;
          bool                    rollback;
          bool                    single;
          bool                    bringup;
          struct hlist_node       *node;
          struct hlist_node       *last;
          enum cpuhp_state        cb_state;
          int                     result;
          atomic_t                ap_sync_state;
          struct completion       done_up;
          struct completion       done_down;
  #endif
  };
  
  static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
          .fail = CPUHP_INVALID,
  };
  
  #ifdef CONFIG_SMP
  cpumask_t cpus_booted_once_mask;
  #endif
  
  #if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
  static struct lockdep_map cpuhp_state_up_map =
          STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
  static struct lockdep_map cpuhp_state_down_map =
          STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);
  
 
 static inline void cpuhp_lock_acquire(bool bringup)
 {
         lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
 }
 
 static inline void cpuhp_lock_release(bool bringup)
 {
         lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
 }
 #else
 
 static inline void cpuhp_lock_acquire(bool bringup) { }
 static inline void cpuhp_lock_release(bool bringup) { }
 
 #endif
 
 /**
  * struct cpuhp_step - Hotplug state machine step
  * @name:       Name of the step
  * @startup:    Startup function of the step
  * @teardown:   Teardown function of the step
  * @cant_stop:  Bringup/teardown can't be stopped at this step
  * @multi_instance:     State has multiple instances which get added afterwards
  */
 struct cpuhp_step {
         const char              *name;
         union {
                 int             (*single)(unsigned int cpu);
                 int             (*multi)(unsigned int cpu,
                                          struct hlist_node *node);
         } startup;
         union {
                 int             (*single)(unsigned int cpu);
                 int             (*multi)(unsigned int cpu,
                                          struct hlist_node *node);
         } teardown;
         /* private: */
         struct hlist_head       list;
         /* public: */
         bool                    cant_stop;
         bool                    multi_instance;
 };
 
 static DEFINE_MUTEX(cpuhp_state_mutex);
 static struct cpuhp_step cpuhp_hp_states[];
 
 static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
 {
         return cpuhp_hp_states + state;
 }
 
 static bool cpuhp_step_empty(bool bringup, struct cpuhp_step *step)
 {
         return bringup ? !step->startup.single : !step->teardown.single;
 }
 
 /**
  * cpuhp_invoke_callback - Invoke the callbacks for a given state
  * @cpu:        The cpu for which the callback should be invoked
  * @state:      The state to do callbacks for
  * @bringup:    True if the bringup callback should be invoked
  * @node:       For multi-instance, do a single entry callback for install/remove
  * @lastp:      For multi-instance rollback, remember how far we got
  *
  * Called from cpu hotplug and from the state register machinery.
  *
  * Return: %0 on success or a negative errno code
  */
 static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
                                  bool bringup, struct hlist_node *node,
                                  struct hlist_node **lastp)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         struct cpuhp_step *step = cpuhp_get_step(state);
         int (*cbm)(unsigned int cpu, struct hlist_node *node);
         int (*cb)(unsigned int cpu);
         int ret, cnt;
 
         if (st->fail == state) {
                 st->fail = CPUHP_INVALID;
                 return -EAGAIN;
         }
 
         if (cpuhp_step_empty(bringup, step)) {
                 WARN_ON_ONCE(1);
                 return 0;
         }
 
         if (!step->multi_instance) {
                 WARN_ON_ONCE(lastp && *lastp);
                 cb = bringup ? step->startup.single : step->teardown.single;
 
                 trace_cpuhp_enter(cpu, st->target, state, cb);
                 ret = cb(cpu);
                 trace_cpuhp_exit(cpu, st->state, state, ret);
                 return ret;
         }
         cbm = bringup ? step->startup.multi : step->teardown.multi;
 
         /* Single invocation for instance add/remove */
         if (node) {
                 WARN_ON_ONCE(lastp && *lastp);
                 trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
                 ret = cbm(cpu, node);
                 trace_cpuhp_exit(cpu, st->state, state, ret);
                 return ret;
         }
 
         /* State transition. Invoke on all instances */
         cnt = 0;
         hlist_for_each(node, &step->list) {
                 if (lastp && node == *lastp)
                         break;
 
                 trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
                 ret = cbm(cpu, node);
                 trace_cpuhp_exit(cpu, st->state, state, ret);
                 if (ret) {
                         if (!lastp)
                                 goto err;
 
                         *lastp = node;
                         return ret;
                 }
                 cnt++;
         }
         if (lastp)
                 *lastp = NULL;
         return 0;
 err:
         /* Rollback the instances if one failed */
         cbm = !bringup ? step->startup.multi : step->teardown.multi;
         if (!cbm)
                 return ret;
 
         hlist_for_each(node, &step->list) {
                 if (!cnt--)
                         break;
 
                 trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
                 ret = cbm(cpu, node);
                 trace_cpuhp_exit(cpu, st->state, state, ret);
                 /*
                  * Rollback must not fail,
                  */
                 WARN_ON_ONCE(ret);
         }
         return ret;
 }
 
 #ifdef CONFIG_SMP
 static bool cpuhp_is_ap_state(enum cpuhp_state state)
 {
         /*
          * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
          * purposes as that state is handled explicitly in cpu_down.
          */
         return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
 }
 
 static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
 {
         struct completion *done = bringup ? &st->done_up : &st->done_down;
         wait_for_completion(done);
 }
 
 static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
 {
         struct completion *done = bringup ? &st->done_up : &st->done_down;
         complete(done);
 }
 
 /*
  * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
  */
 static bool cpuhp_is_atomic_state(enum cpuhp_state state)
 {
         return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
 }
 
 /* Synchronization state management */
 enum cpuhp_sync_state {
         SYNC_STATE_DEAD,
         SYNC_STATE_KICKED,
         SYNC_STATE_SHOULD_DIE,
         SYNC_STATE_ALIVE,
         SYNC_STATE_SHOULD_ONLINE,
         SYNC_STATE_ONLINE,
 };
 
 #ifdef CONFIG_HOTPLUG_CORE_SYNC
 /**
  * cpuhp_ap_update_sync_state - Update synchronization state during bringup/teardown
  * @state:      The synchronization state to set
  *
  * No synchronization point. Just update of the synchronization state, but implies
  * a full barrier so that the AP changes are visible before the control CPU proceeds.
  */
 static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
 {
         atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
 
         (void)atomic_xchg(st, state);
 }
 
 void __weak arch_cpuhp_sync_state_poll(void) { cpu_relax(); }
 
 static bool cpuhp_wait_for_sync_state(unsigned int cpu, enum cpuhp_sync_state state,
                                       enum cpuhp_sync_state next_state)
 {
         atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
         ktime_t now, end, start = ktime_get();
         int sync;
 
         end = start + 10ULL * NSEC_PER_SEC;
 
         sync = atomic_read(st);
         while (1) {
                 if (sync == state) {
                         if (!atomic_try_cmpxchg(st, &sync, next_state))
                                 continue;
                         return true;
                 }
 
                 now = ktime_get();
                 if (now > end) {
                         /* Timeout. Leave the state unchanged */
                         return false;
                 } else if (now - start < NSEC_PER_MSEC) {
                         /* Poll for one millisecond */
                         arch_cpuhp_sync_state_poll();
                 } else {
                         usleep_range_state(USEC_PER_MSEC, 2 * USEC_PER_MSEC, TASK_UNINTERRUPTIBLE);
                 }
                 sync = atomic_read(st);
         }
         return true;
 }
 #else  /* CONFIG_HOTPLUG_CORE_SYNC */
 static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state) { }
 #endif /* !CONFIG_HOTPLUG_CORE_SYNC */
 
 #ifdef CONFIG_HOTPLUG_CORE_SYNC_DEAD
 /**
  * cpuhp_ap_report_dead - Update synchronization state to DEAD
  *
  * No synchronization point. Just update of the synchronization state.
  */
 void cpuhp_ap_report_dead(void)
 {
         cpuhp_ap_update_sync_state(SYNC_STATE_DEAD);
 }
 
 void __weak arch_cpuhp_cleanup_dead_cpu(unsigned int cpu) { }
 
 /*
  * Late CPU shutdown synchronization point. Cannot use cpuhp_state::done_down
  * because the AP cannot issue complete() at this stage.
  */
 static void cpuhp_bp_sync_dead(unsigned int cpu)
 {
         atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
         int sync = atomic_read(st);
 
         do {
                 /* CPU can have reported dead already. Don't overwrite that! */
                 if (sync == SYNC_STATE_DEAD)
                         break;
         } while (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_SHOULD_DIE));
 
         if (cpuhp_wait_for_sync_state(cpu, SYNC_STATE_DEAD, SYNC_STATE_DEAD)) {
                 /* CPU reached dead state. Invoke the cleanup function */
                 arch_cpuhp_cleanup_dead_cpu(cpu);
                 return;
         }
 
         /* No further action possible. Emit message and give up. */
         pr_err("CPU%u failed to report dead state\n", cpu);
 }
 #else /* CONFIG_HOTPLUG_CORE_SYNC_DEAD */
 static inline void cpuhp_bp_sync_dead(unsigned int cpu) { }
 #endif /* !CONFIG_HOTPLUG_CORE_SYNC_DEAD */
 
 #ifdef CONFIG_HOTPLUG_CORE_SYNC_FULL
 /**
  * cpuhp_ap_sync_alive - Synchronize AP with the control CPU once it is alive
  *
  * Updates the AP synchronization state to SYNC_STATE_ALIVE and waits
  * for the BP to release it.
  */
 void cpuhp_ap_sync_alive(void)
 {
         atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
 
         cpuhp_ap_update_sync_state(SYNC_STATE_ALIVE);
 
         /* Wait for the control CPU to release it. */
         while (atomic_read(st) != SYNC_STATE_SHOULD_ONLINE)
                 cpu_relax();
 }
 
 static bool cpuhp_can_boot_ap(unsigned int cpu)
 {
         atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
         int sync = atomic_read(st);
 
 again:
         switch (sync) {
         case SYNC_STATE_DEAD:
                 /* CPU is properly dead */
                 break;
         case SYNC_STATE_KICKED:
                 /* CPU did not come up in previous attempt */
                 break;
         case SYNC_STATE_ALIVE:
                 /* CPU is stuck cpuhp_ap_sync_alive(). */
                 break;
         default:
                 /* CPU failed to report online or dead and is in limbo state. */
                 return false;
         }
 
         /* Prepare for booting */
         if (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_KICKED))
                 goto again;
 
         return true;
 }
 
 void __weak arch_cpuhp_cleanup_kick_cpu(unsigned int cpu) { }
 
 /*
  * Early CPU bringup synchronization point. Cannot use cpuhp_state::done_up
  * because the AP cannot issue complete() so early in the bringup.
  */
 static int cpuhp_bp_sync_alive(unsigned int cpu)
 {
         int ret = 0;
 
         if (!IS_ENABLED(CONFIG_HOTPLUG_CORE_SYNC_FULL))
                 return 0;
 
         if (!cpuhp_wait_for_sync_state(cpu, SYNC_STATE_ALIVE, SYNC_STATE_SHOULD_ONLINE)) {
                 pr_err("CPU%u failed to report alive state\n", cpu);
                 ret = -EIO;
         }
 
         /* Let the architecture cleanup the kick alive mechanics. */
         arch_cpuhp_cleanup_kick_cpu(cpu);
         return ret;
 }
 #else /* CONFIG_HOTPLUG_CORE_SYNC_FULL */
 static inline int cpuhp_bp_sync_alive(unsigned int cpu) { return 0; }
 static inline bool cpuhp_can_boot_ap(unsigned int cpu) { return true; }
 #endif /* !CONFIG_HOTPLUG_CORE_SYNC_FULL */
 
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
 bool cpuhp_tasks_frozen;
 EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);
 
 /*
  * The following two APIs (cpu_maps_update_begin/done) must be used when
  * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
  */
 void cpu_maps_update_begin(void)
 {
         mutex_lock(&cpu_add_remove_lock);
 }
 
 void cpu_maps_update_done(void)
 {
         mutex_unlock(&cpu_add_remove_lock);
 }
 
 /*
  * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  * Should always be manipulated under cpu_add_remove_lock
  */
 static int cpu_hotplug_disabled;
 
 #ifdef CONFIG_HOTPLUG_CPU
 
 DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
 
 static bool cpu_hotplug_offline_disabled __ro_after_init;
 
 void cpus_read_lock(void)
 {
         percpu_down_read(&cpu_hotplug_lock);
 }
 EXPORT_SYMBOL_GPL(cpus_read_lock);
 
 int cpus_read_trylock(void)
 {
         return percpu_down_read_trylock(&cpu_hotplug_lock);
 }
 EXPORT_SYMBOL_GPL(cpus_read_trylock);
 
 void cpus_read_unlock(void)
 {
         percpu_up_read(&cpu_hotplug_lock);
 }
 EXPORT_SYMBOL_GPL(cpus_read_unlock);
 
 void cpus_write_lock(void)
 {
         percpu_down_write(&cpu_hotplug_lock);
 }
 
 void cpus_write_unlock(void)
 {
         percpu_up_write(&cpu_hotplug_lock);
 }
 
 void lockdep_assert_cpus_held(void)
 {
         /*
          * We can't have hotplug operations before userspace starts running,
          * and some init codepaths will knowingly not take the hotplug lock.
          * This is all valid, so mute lockdep until it makes sense to report
          * unheld locks.
          */
         if (system_state < SYSTEM_RUNNING)
                 return;
 
         percpu_rwsem_assert_held(&cpu_hotplug_lock);
 }
 
 #ifdef CONFIG_LOCKDEP
 int lockdep_is_cpus_held(void)
 {
         return percpu_rwsem_is_held(&cpu_hotplug_lock);
 }
 #endif
 
 static void lockdep_acquire_cpus_lock(void)
 {
         rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
 }
 
 static void lockdep_release_cpus_lock(void)
 {
         rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
 }
 
 /* Declare CPU offlining not supported */
 void cpu_hotplug_disable_offlining(void)
 {
         cpu_maps_update_begin();
         cpu_hotplug_offline_disabled = true;
         cpu_maps_update_done();
 }
 
 /*
  * Wait for currently running CPU hotplug operations to complete (if any) and
  * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
  * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
  * hotplug path before performing hotplug operations. So acquiring that lock
  * guarantees mutual exclusion from any currently running hotplug operations.
  */
 void cpu_hotplug_disable(void)
 {
         cpu_maps_update_begin();
         cpu_hotplug_disabled++;
         cpu_maps_update_done();
 }
 EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
 
 static void __cpu_hotplug_enable(void)
 {
         if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n"))
                 return;
         cpu_hotplug_disabled--;
 }
 
 void cpu_hotplug_enable(void)
 {
         cpu_maps_update_begin();
         __cpu_hotplug_enable();
         cpu_maps_update_done();
 }
 EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
 
 #else
 
 static void lockdep_acquire_cpus_lock(void)
 {
 }
 
 static void lockdep_release_cpus_lock(void)
 {
 }
 
 #endif  /* CONFIG_HOTPLUG_CPU */
 
 /*
  * Architectures that need SMT-specific errata handling during SMT hotplug
  * should override this.
  */
 void __weak arch_smt_update(void) { }
 
 #ifdef CONFIG_HOTPLUG_SMT
 
 enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
 static unsigned int cpu_smt_max_threads __ro_after_init;
 unsigned int cpu_smt_num_threads __read_mostly = UINT_MAX;
 
 void __init cpu_smt_disable(bool force)
 {
         if (!cpu_smt_possible())
                 return;
 
         if (force) {
                 pr_info("SMT: Force disabled\n");
                 cpu_smt_control = CPU_SMT_FORCE_DISABLED;
         } else {
                 pr_info("SMT: disabled\n");
                 cpu_smt_control = CPU_SMT_DISABLED;
         }
         cpu_smt_num_threads = 1;
 }
 
 /*
  * The decision whether SMT is supported can only be done after the full
  * CPU identification. Called from architecture code.
  */
 void __init cpu_smt_set_num_threads(unsigned int num_threads,
                                     unsigned int max_threads)
 {
         WARN_ON(!num_threads || (num_threads > max_threads));
 
         if (max_threads == 1)
                 cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
 
         cpu_smt_max_threads = max_threads;
 
         /*
          * If SMT has been disabled via the kernel command line or SMT is
          * not supported, set cpu_smt_num_threads to 1 for consistency.
          * If enabled, take the architecture requested number of threads
          * to bring up into account.
          */
         if (cpu_smt_control != CPU_SMT_ENABLED)
                 cpu_smt_num_threads = 1;
         else if (num_threads < cpu_smt_num_threads)
                 cpu_smt_num_threads = num_threads;
 }
 
 static int __init smt_cmdline_disable(char *str)
 {
         cpu_smt_disable(str && !strcmp(str, "force"));
         return 0;
 }
 early_param("nosmt", smt_cmdline_disable);
 
 /*
  * For Archicture supporting partial SMT states check if the thread is allowed.
  * Otherwise this has already been checked through cpu_smt_max_threads when
  * setting the SMT level.
  */
 static inline bool cpu_smt_thread_allowed(unsigned int cpu)
 {
 #ifdef CONFIG_SMT_NUM_THREADS_DYNAMIC
         return topology_smt_thread_allowed(cpu);
 #else
         return true;
 #endif
 }
 
 static inline bool cpu_bootable(unsigned int cpu)
 {
         if (cpu_smt_control == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
                 return true;
 
         /* All CPUs are bootable if controls are not configured */
         if (cpu_smt_control == CPU_SMT_NOT_IMPLEMENTED)
                 return true;
 
         /* All CPUs are bootable if CPU is not SMT capable */
         if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
                 return true;
 
         if (topology_is_primary_thread(cpu))
                 return true;
 
         /*
          * On x86 it's required to boot all logical CPUs at least once so
          * that the init code can get a chance to set CR4.MCE on each
          * CPU. Otherwise, a broadcasted MCE observing CR4.MCE=0b on any
          * core will shutdown the machine.
          */
         return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
 }
 
 /* Returns true if SMT is supported and not forcefully (irreversibly) disabled */
 bool cpu_smt_possible(void)
 {
         return cpu_smt_control != CPU_SMT_FORCE_DISABLED &&
                 cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
 }
 EXPORT_SYMBOL_GPL(cpu_smt_possible);
 
 #else
 static inline bool cpu_bootable(unsigned int cpu) { return true; }
 #endif
 
 static inline enum cpuhp_state
 cpuhp_set_state(int cpu, struct cpuhp_cpu_state *st, enum cpuhp_state target)
 {
         enum cpuhp_state prev_state = st->state;
         bool bringup = st->state < target;
 
         st->rollback = false;
         st->last = NULL;
 
         st->target = target;
         st->single = false;
         st->bringup = bringup;
         if (cpu_dying(cpu) != !bringup)
                 set_cpu_dying(cpu, !bringup);
 
         return prev_state;
 }
 
 static inline void
 cpuhp_reset_state(int cpu, struct cpuhp_cpu_state *st,
                   enum cpuhp_state prev_state)
 {
         bool bringup = !st->bringup;
 
         st->target = prev_state;
 
         /*
          * Already rolling back. No need invert the bringup value or to change
          * the current state.
          */
         if (st->rollback)
                 return;
 
         st->rollback = true;
 
         /*
          * If we have st->last we need to undo partial multi_instance of this
          * state first. Otherwise start undo at the previous state.
          */
         if (!st->last) {
                 if (st->bringup)
                         st->state--;
                 else
                         st->state++;
         }
 
         st->bringup = bringup;
         if (cpu_dying(cpu) != !bringup)
                 set_cpu_dying(cpu, !bringup);
 }
 
 /* Regular hotplug invocation of the AP hotplug thread */
 static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
 {
         if (!st->single && st->state == st->target)
                 return;
 
         st->result = 0;
         /*
          * Make sure the above stores are visible before should_run becomes
          * true. Paired with the mb() above in cpuhp_thread_fun()
          */
         smp_mb();
         st->should_run = true;
         wake_up_process(st->thread);
         wait_for_ap_thread(st, st->bringup);
 }
 
 static int cpuhp_kick_ap(int cpu, struct cpuhp_cpu_state *st,
                          enum cpuhp_state target)
 {
         enum cpuhp_state prev_state;
         int ret;
 
         prev_state = cpuhp_set_state(cpu, st, target);
         __cpuhp_kick_ap(st);
         if ((ret = st->result)) {
                 cpuhp_reset_state(cpu, st, prev_state);
                 __cpuhp_kick_ap(st);
         }
 
         return ret;
 }
 
 static int bringup_wait_for_ap_online(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
         /* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
         wait_for_ap_thread(st, true);
         if (WARN_ON_ONCE((!cpu_online(cpu))))
                 return -ECANCELED;
 
         /* Unpark the hotplug thread of the target cpu */
         kthread_unpark(st->thread);
 
         /*
          * SMT soft disabling on X86 requires to bring the CPU out of the
          * BIOS 'wait for SIPI' state in order to set the CR4.MCE bit.  The
          * CPU marked itself as booted_once in notify_cpu_starting() so the
          * cpu_bootable() check will now return false if this is not the
          * primary sibling.
          */
         if (!cpu_bootable(cpu))
                 return -ECANCELED;
         return 0;
 }
 
 #ifdef CONFIG_HOTPLUG_SPLIT_STARTUP
 static int cpuhp_kick_ap_alive(unsigned int cpu)
 {
         if (!cpuhp_can_boot_ap(cpu))
                 return -EAGAIN;
 
         return arch_cpuhp_kick_ap_alive(cpu, idle_thread_get(cpu));
 }
 
 static int cpuhp_bringup_ap(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int ret;
 
         /*
          * Some architectures have to walk the irq descriptors to
          * setup the vector space for the cpu which comes online.
          * Prevent irq alloc/free across the bringup.
          */
         irq_lock_sparse();
 
         ret = cpuhp_bp_sync_alive(cpu);
         if (ret)
                 goto out_unlock;
 
         ret = bringup_wait_for_ap_online(cpu);
         if (ret)
                 goto out_unlock;
 
         irq_unlock_sparse();
 
         if (st->target <= CPUHP_AP_ONLINE_IDLE)
                 return 0;
 
         return cpuhp_kick_ap(cpu, st, st->target);
 
 out_unlock:
         irq_unlock_sparse();
         return ret;
 }
 #else
 static int bringup_cpu(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         struct task_struct *idle = idle_thread_get(cpu);
         int ret;
 
         if (!cpuhp_can_boot_ap(cpu))
                 return -EAGAIN;
 
         /*
          * Some architectures have to walk the irq descriptors to
          * setup the vector space for the cpu which comes online.
          *
          * Prevent irq alloc/free across the bringup by acquiring the
          * sparse irq lock. Hold it until the upcoming CPU completes the
          * startup in cpuhp_online_idle() which allows to avoid
          * intermediate synchronization points in the architecture code.
          */
         irq_lock_sparse();
 
         ret = __cpu_up(cpu, idle);
         if (ret)
                 goto out_unlock;
 
         ret = cpuhp_bp_sync_alive(cpu);
         if (ret)
                 goto out_unlock;
 
         ret = bringup_wait_for_ap_online(cpu);
         if (ret)
                 goto out_unlock;
 
         irq_unlock_sparse();
 
         if (st->target <= CPUHP_AP_ONLINE_IDLE)
                 return 0;
 
         return cpuhp_kick_ap(cpu, st, st->target);
 
 out_unlock:
         irq_unlock_sparse();
         return ret;
 }
 #endif
 
 static int finish_cpu(unsigned int cpu)
 {
         struct task_struct *idle = idle_thread_get(cpu);
         struct mm_struct *mm = idle->active_mm;
 
         /*
          * idle_task_exit() will have switched to &init_mm, now
          * clean up any remaining active_mm state.
          */
         if (mm != &init_mm)
                 idle->active_mm = &init_mm;
         mmdrop_lazy_tlb(mm);
         return 0;
 }
 
 /*
  * Hotplug state machine related functions
  */
 
 /*
  * Get the next state to run. Empty ones will be skipped. Returns true if a
  * state must be run.
  *
  * st->state will be modified ahead of time, to match state_to_run, as if it
  * has already ran.
  */
 static bool cpuhp_next_state(bool bringup,
                              enum cpuhp_state *state_to_run,
                              struct cpuhp_cpu_state *st,
                              enum cpuhp_state target)
 {
         do {
                 if (bringup) {
                         if (st->state >= target)
                                 return false;
 
                         *state_to_run = ++st->state;
                 } else {
                         if (st->state <= target)
                                 return false;
 
                         *state_to_run = st->state--;
                 }
 
                 if (!cpuhp_step_empty(bringup, cpuhp_get_step(*state_to_run)))
                         break;
         } while (true);
 
         return true;
 }
 
 static int __cpuhp_invoke_callback_range(bool bringup,
                                          unsigned int cpu,
                                          struct cpuhp_cpu_state *st,
                                          enum cpuhp_state target,
                                          bool nofail)
 {
         enum cpuhp_state state;
         int ret = 0;
 
         while (cpuhp_next_state(bringup, &state, st, target)) {
                 int err;
 
                 err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
                 if (!err)
                         continue;
 
                 if (nofail) {
                         pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
                                 cpu, bringup ? "UP" : "DOWN",
                                 cpuhp_get_step(st->state)->name,
                                 st->state, err);
                         ret = -1;
                 } else {
                         ret = err;
                         break;
                 }
         }
 
         return ret;
 }
 
 static inline int cpuhp_invoke_callback_range(bool bringup,
                                               unsigned int cpu,
                                               struct cpuhp_cpu_state *st,
                                               enum cpuhp_state target)
 {
         return __cpuhp_invoke_callback_range(bringup, cpu, st, target, false);
 }
 
 static inline void cpuhp_invoke_callback_range_nofail(bool bringup,
                                                       unsigned int cpu,
                                                       struct cpuhp_cpu_state *st,
                                                       enum cpuhp_state target)
 {
         __cpuhp_invoke_callback_range(bringup, cpu, st, target, true);
 }
 
 static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
 {
         if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
                 return true;
         /*
          * When CPU hotplug is disabled, then taking the CPU down is not
          * possible because takedown_cpu() and the architecture and
          * subsystem specific mechanisms are not available. So the CPU
          * which would be completely unplugged again needs to stay around
          * in the current state.
          */
         return st->state <= CPUHP_BRINGUP_CPU;
 }
 
 static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                               enum cpuhp_state target)
 {
         enum cpuhp_state prev_state = st->state;
         int ret = 0;
 
         ret = cpuhp_invoke_callback_range(true, cpu, st, target);
         if (ret) {
                 pr_debug("CPU UP failed (%d) CPU %u state %s (%d)\n",
                          ret, cpu, cpuhp_get_step(st->state)->name,
                          st->state);
 
                 cpuhp_reset_state(cpu, st, prev_state);
                 if (can_rollback_cpu(st))
                         WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
                                                             prev_state));
         }
         return ret;
 }
 
 /*
  * The cpu hotplug threads manage the bringup and teardown of the cpus
  */
 static int cpuhp_should_run(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
         return st->should_run;
 }
 
 /*
  * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
  * callbacks when a state gets [un]installed at runtime.
  *
  * Each invocation of this function by the smpboot thread does a single AP
  * state callback.
  *
  * It has 3 modes of operation:
  *  - single: runs st->cb_state
  *  - up:     runs ++st->state, while st->state < st->target
  *  - down:   runs st->state--, while st->state > st->target
  *
  * When complete or on error, should_run is cleared and the completion is fired.
  */
 static void cpuhp_thread_fun(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
         bool bringup = st->bringup;
         enum cpuhp_state state;
 
         if (WARN_ON_ONCE(!st->should_run))
                 return;
 
         /*
          * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
          * that if we see ->should_run we also see the rest of the state.
          */
         smp_mb();
 
         /*
          * The BP holds the hotplug lock, but we're now running on the AP,
          * ensure that anybody asserting the lock is held, will actually find
          * it so.
          */
         lockdep_acquire_cpus_lock();
         cpuhp_lock_acquire(bringup);
 
         if (st->single) {
                 state = st->cb_state;
                 st->should_run = false;
         } else {
                 st->should_run = cpuhp_next_state(bringup, &state, st, st->target);
                 if (!st->should_run)
                         goto end;
         }
 
         WARN_ON_ONCE(!cpuhp_is_ap_state(state));
 
         if (cpuhp_is_atomic_state(state)) {
                 local_irq_disable();
                 st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
                 local_irq_enable();
 
                 /*
                  * STARTING/DYING must not fail!
                  */
                 WARN_ON_ONCE(st->result);
         } else {
                 st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
         }
 
         if (st->result) {
                 /*
                  * If we fail on a rollback, we're up a creek without no
                  * paddle, no way forward, no way back. We loose, thanks for
                  * playing.
                  */
                 WARN_ON_ONCE(st->rollback);
                 st->should_run = false;
         }
 
 end:
         cpuhp_lock_release(bringup);
         lockdep_release_cpus_lock();
 
         if (!st->should_run)
                 complete_ap_thread(st, bringup);
 }
 
 /* Invoke a single callback on a remote cpu */
 static int
 cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
                          struct hlist_node *node)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int ret;
 
         if (!cpu_online(cpu))
                 return 0;
 
         cpuhp_lock_acquire(false);
         cpuhp_lock_release(false);
 
         cpuhp_lock_acquire(true);
         cpuhp_lock_release(true);
 
         /*
          * If we are up and running, use the hotplug thread. For early calls
          * we invoke the thread function directly.
          */
         if (!st->thread)
                 return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
 
         st->rollback = false;
         st->last = NULL;
 
         st->node = node;
         st->bringup = bringup;
         st->cb_state = state;
         st->single = true;
 
         __cpuhp_kick_ap(st);
 
         /*
          * If we failed and did a partial, do a rollback.
          */
         if ((ret = st->result) && st->last) {
                 st->rollback = true;
                 st->bringup = !bringup;
 
                 __cpuhp_kick_ap(st);
         }
 
         /*
          * Clean up the leftovers so the next hotplug operation wont use stale
          * data.
          */
         st->node = st->last = NULL;
         return ret;
 }
 
 static int cpuhp_kick_ap_work(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         enum cpuhp_state prev_state = st->state;
         int ret;
 
         cpuhp_lock_acquire(false);
         cpuhp_lock_release(false);
 
         cpuhp_lock_acquire(true);
         cpuhp_lock_release(true);
 
         trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
         ret = cpuhp_kick_ap(cpu, st, st->target);
         trace_cpuhp_exit(cpu, st->state, prev_state, ret);
 
         return ret;
 }
 
 static struct smp_hotplug_thread cpuhp_threads = {
         .store                  = &cpuhp_state.thread,
         .thread_should_run      = cpuhp_should_run,
         .thread_fn              = cpuhp_thread_fun,
         .thread_comm            = "cpuhp/%u",
         .selfparking            = true,
 };
 
 static __init void cpuhp_init_state(void)
 {
         struct cpuhp_cpu_state *st;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 st = per_cpu_ptr(&cpuhp_state, cpu);
                 init_completion(&st->done_up);
                 init_completion(&st->done_down);
         }
 }
 
 void __init cpuhp_threads_init(void)
 {
         cpuhp_init_state();
         BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
         kthread_unpark(this_cpu_read(cpuhp_state.thread));
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
 #ifndef arch_clear_mm_cpumask_cpu
 #define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
 #endif
 
 /**
  * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
  * @cpu: a CPU id
  *
  * This function walks all processes, finds a valid mm struct for each one and
  * then clears a corresponding bit in mm's cpumask.  While this all sounds
  * trivial, there are various non-obvious corner cases, which this function
  * tries to solve in a safe manner.
  *
  * Also note that the function uses a somewhat relaxed locking scheme, so it may
  * be called only for an already offlined CPU.
  */
 void clear_tasks_mm_cpumask(int cpu)
 {
         struct task_struct *p;
 
         /*
          * This function is called after the cpu is taken down and marked
          * offline, so its not like new tasks will ever get this cpu set in
          * their mm mask. -- Peter Zijlstra
          * Thus, we may use rcu_read_lock() here, instead of grabbing
          * full-fledged tasklist_lock.
          */
         WARN_ON(cpu_online(cpu));
         rcu_read_lock();
         for_each_process(p) {
                 struct task_struct *t;
 
                 /*
                  * Main thread might exit, but other threads may still have
                  * a valid mm. Find one.
                  */
                 t = find_lock_task_mm(p);
                 if (!t)
                         continue;
                 arch_clear_mm_cpumask_cpu(cpu, t->mm);
                 task_unlock(t);
         }
         rcu_read_unlock();
 }
 
 /* Take this CPU down. */
 static int take_cpu_down(void *_param)
 {
         struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
         enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
         int err, cpu = smp_processor_id();
 
         /* Ensure this CPU doesn't handle any more interrupts. */
         err = __cpu_disable();
         if (err < 0)
                 return err;
 
         /*
          * Must be called from CPUHP_TEARDOWN_CPU, which means, as we are going
          * down, that the current state is CPUHP_TEARDOWN_CPU - 1.
          */
         WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));
 
         /*
          * Invoke the former CPU_DYING callbacks. DYING must not fail!
          */
         cpuhp_invoke_callback_range_nofail(false, cpu, st, target);
 
         /* Park the stopper thread */
         stop_machine_park(cpu);
         return 0;
 }
 
 static int takedown_cpu(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int err;
 
         /* Park the smpboot threads */
         kthread_park(st->thread);
 
         /*
          * Prevent irq alloc/free while the dying cpu reorganizes the
          * interrupt affinities.
          */
         irq_lock_sparse();
 
         /*
          * So now all preempt/rcu users must observe !cpu_active().
          */
         err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
         if (err) {
                 /* CPU refused to die */
                 irq_unlock_sparse();
                 /* Unpark the hotplug thread so we can rollback there */
                 kthread_unpark(st->thread);
                 return err;
         }
         BUG_ON(cpu_online(cpu));
 
         /*
          * The teardown callback for CPUHP_AP_SCHED_STARTING will have removed
          * all runnable tasks from the CPU, there's only the idle task left now
          * that the migration thread is done doing the stop_machine thing.
          *
          * Wait for the stop thread to go away.
          */
         wait_for_ap_thread(st, false);
         BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
 
         /* Interrupts are moved away from the dying cpu, reenable alloc/free */
         irq_unlock_sparse();
 
         hotplug_cpu__broadcast_tick_pull(cpu);
         /* This actually kills the CPU. */
         __cpu_die(cpu);
 
         cpuhp_bp_sync_dead(cpu);
 
         tick_cleanup_dead_cpu(cpu);
 
         /*
          * Callbacks must be re-integrated right away to the RCU state machine.
          * Otherwise an RCU callback could block a further teardown function
          * waiting for its completion.
          */
         rcutree_migrate_callbacks(cpu);
 
         return 0;
 }
 
 static void cpuhp_complete_idle_dead(void *arg)
 {
         struct cpuhp_cpu_state *st = arg;
 
         complete_ap_thread(st, false);
 }
 
 void cpuhp_report_idle_dead(void)
 {
         struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
         BUG_ON(st->state != CPUHP_AP_OFFLINE);
         tick_assert_timekeeping_handover();
         rcutree_report_cpu_dead();
         st->state = CPUHP_AP_IDLE_DEAD;
         /*
          * We cannot call complete after rcutree_report_cpu_dead() so we delegate it
          * to an online cpu.
          */
         smp_call_function_single(cpumask_first(cpu_online_mask),
                                  cpuhp_complete_idle_dead, st, 0);
 }
 
 static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                                 enum cpuhp_state target)
 {
         enum cpuhp_state prev_state = st->state;
         int ret = 0;
 
         ret = cpuhp_invoke_callback_range(false, cpu, st, target);
         if (ret) {
                 pr_debug("CPU DOWN failed (%d) CPU %u state %s (%d)\n",
                          ret, cpu, cpuhp_get_step(st->state)->name,
                          st->state);
 
                 cpuhp_reset_state(cpu, st, prev_state);
 
                 if (st->state < prev_state)
                         WARN_ON(cpuhp_invoke_callback_range(true, cpu, st,
                                                             prev_state));
         }
 
         return ret;
 }
 
 /* Requires cpu_add_remove_lock to be held */
 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
                            enum cpuhp_state target)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         int prev_state, ret = 0;
 
         if (num_online_cpus() == 1)
                 return -EBUSY;
 
         if (!cpu_present(cpu))
                 return -EINVAL;
 
         cpus_write_lock();
 
         cpuhp_tasks_frozen = tasks_frozen;
 
         prev_state = cpuhp_set_state(cpu, st, target);
         /*
          * If the current CPU state is in the range of the AP hotplug thread,
          * then we need to kick the thread.
          */
         if (st->state > CPUHP_TEARDOWN_CPU) {
                 st->target = max((int)target, CPUHP_TEARDOWN_CPU);
                 ret = cpuhp_kick_ap_work(cpu);
                 /*
                  * The AP side has done the error rollback already. Just
                  * return the error code..
                  */
                 if (ret)
                         goto out;
 
                 /*
                  * We might have stopped still in the range of the AP hotplug
                  * thread. Nothing to do anymore.
                  */
                 if (st->state > CPUHP_TEARDOWN_CPU)
                         goto out;
 
                 st->target = target;
         }
         /*
          * The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
          * to do the further cleanups.
          */
         ret = cpuhp_down_callbacks(cpu, st, target);
         if (ret && st->state < prev_state) {
                 if (st->state == CPUHP_TEARDOWN_CPU) {
                         cpuhp_reset_state(cpu, st, prev_state);
                         __cpuhp_kick_ap(st);
                 } else {
                         WARN(1, "DEAD callback error for CPU%d", cpu);
                 }
         }
 
 out:
         cpus_write_unlock();
         /*
          * Do post unplug cleanup. This is still protected against
          * concurrent CPU hotplug via cpu_add_remove_lock.
          */
         lockup_detector_cleanup();
         arch_smt_update();
         return ret;
 }
 
 struct cpu_down_work {
         unsigned int            cpu;
         enum cpuhp_state        target;
 };
 
 static long __cpu_down_maps_locked(void *arg)
 {
         struct cpu_down_work *work = arg;
 
         return _cpu_down(work->cpu, 0, work->target);
 }
 
 static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
 {
         struct cpu_down_work work = { .cpu = cpu, .target = target, };
 
         /*
          * If the platform does not support hotplug, report it explicitly to
          * differentiate it from a transient offlining failure.
          */
         if (cpu_hotplug_offline_disabled)
                 return -EOPNOTSUPP;
         if (cpu_hotplug_disabled)
                 return -EBUSY;
 
         /*
          * Ensure that the control task does not run on the to be offlined
          * CPU to prevent a deadlock against cfs_b->period_timer.
          * Also keep at least one housekeeping cpu onlined to avoid generating
          * an empty sched_domain span.
          */
         for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN)) {
                 if (cpu != work.cpu)
                         return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
         }
         return -EBUSY;
 }
 
 static int cpu_down(unsigned int cpu, enum cpuhp_state target)
 {
         int err;
 
         cpu_maps_update_begin();
         err = cpu_down_maps_locked(cpu, target);
         cpu_maps_update_done();
         return err;
 }
 
 /**
  * cpu_device_down - Bring down a cpu device
  * @dev: Pointer to the cpu device to offline
  *
  * This function is meant to be used by device core cpu subsystem only.
  *
  * Other subsystems should use remove_cpu() instead.
  *
  * Return: %0 on success or a negative errno code
  */
 int cpu_device_down(struct device *dev)
 {
         return cpu_down(dev->id, CPUHP_OFFLINE);
 }
 
 int remove_cpu(unsigned int cpu)
 {
         int ret;
 
         lock_device_hotplug();
         ret = device_offline(get_cpu_device(cpu));
         unlock_device_hotplug();
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(remove_cpu);
 
 void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
 {
         unsigned int cpu;
         int error;
 
         cpu_maps_update_begin();
 
         /*
          * Make certain the cpu I'm about to reboot on is online.
          *
          * This is inline to what migrate_to_reboot_cpu() already do.
          */
         if (!cpu_online(primary_cpu))
                 primary_cpu = cpumask_first(cpu_online_mask);
 
         for_each_online_cpu(cpu) {
                 if (cpu == primary_cpu)
                         continue;
 
                 error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
                 if (error) {
                         pr_err("Failed to offline CPU%d - error=%d",
                                 cpu, error);
                         break;
                 }
         }
 
         /*
          * Ensure all but the reboot CPU are offline.
          */
         BUG_ON(num_online_cpus() > 1);
 
         /*
          * Make sure the CPUs won't be enabled by someone else after this
          * point. Kexec will reboot to a new kernel shortly resetting
          * everything along the way.
          */
         cpu_hotplug_disabled++;
 
         cpu_maps_update_done();
 }
 
 #else
 #define takedown_cpu            NULL
 #endif /*CONFIG_HOTPLUG_CPU*/
 
 /**
  * notify_cpu_starting(cpu) - Invoke the callbacks on the starting CPU
  * @cpu: cpu that just started
  *
  * It must be called by the arch code on the new cpu, before the new cpu
  * enables interrupts and before the "boot" cpu returns from __cpu_up().
  */
 void notify_cpu_starting(unsigned int cpu)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
 
         rcutree_report_cpu_starting(cpu);       /* Enables RCU usage on this CPU. */
         cpumask_set_cpu(cpu, &cpus_booted_once_mask);
 
         /*
          * STARTING must not fail!
          */
         cpuhp_invoke_callback_range_nofail(true, cpu, st, target);
 }
 
 /*
  * Called from the idle task. Wake up the controlling task which brings the
  * hotplug thread of the upcoming CPU up and then delegates the rest of the
  * online bringup to the hotplug thread.
  */
 void cpuhp_online_idle(enum cpuhp_state state)
 {
         struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
         /* Happens for the boot cpu */
         if (state != CPUHP_AP_ONLINE_IDLE)
                 return;
 
         cpuhp_ap_update_sync_state(SYNC_STATE_ONLINE);
 
         /*
          * Unpark the stopper thread before we start the idle loop (and start
          * scheduling); this ensures the stopper task is always available.
          */
         stop_machine_unpark(smp_processor_id());
 
         st->state = CPUHP_AP_ONLINE_IDLE;
         complete_ap_thread(st, true);
 }
 
 /* Requires cpu_add_remove_lock to be held */
 static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         struct task_struct *idle;
         int ret = 0;
 
         cpus_write_lock();
 
         if (!cpu_present(cpu)) {
                 ret = -EINVAL;
                 goto out;
         }
 
         /*
          * The caller of cpu_up() might have raced with another
          * caller. Nothing to do.
          */
         if (st->state >= target)
                 goto out;
 
         if (st->state == CPUHP_OFFLINE) {
                 /* Let it fail before we try to bring the cpu up */
                 idle = idle_thread_get(cpu);
                 if (IS_ERR(idle)) {
                         ret = PTR_ERR(idle);
                         goto out;
                 }
 
                 /*
                  * Reset stale stack state from the last time this CPU was online.
                  */
                 scs_task_reset(idle);
                 kasan_unpoison_task_stack(idle);
         }
 
         cpuhp_tasks_frozen = tasks_frozen;
 
         cpuhp_set_state(cpu, st, target);
         /*
          * If the current CPU state is in the range of the AP hotplug thread,
          * then we need to kick the thread once more.
          */
         if (st->state > CPUHP_BRINGUP_CPU) {
                 ret = cpuhp_kick_ap_work(cpu);
                 /*
                  * The AP side has done the error rollback already. Just
                  * return the error code..
                  */
                 if (ret)
                         goto out;
         }
 
         /*
          * Try to reach the target state. We max out on the BP at
          * CPUHP_BRINGUP_CPU. After that the AP hotplug thread is
          * responsible for bringing it up to the target state.
          */
         target = min((int)target, CPUHP_BRINGUP_CPU);
         ret = cpuhp_up_callbacks(cpu, st, target);
 out:
         cpus_write_unlock();
         arch_smt_update();
         return ret;
 }
 
 static int cpu_up(unsigned int cpu, enum cpuhp_state target)
 {
         int err = 0;
 
         if (!cpu_possible(cpu)) {
                 pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
                        cpu);
                 return -EINVAL;
         }
 
         err = try_online_node(cpu_to_node(cpu));
         if (err)
                 return err;
 
         cpu_maps_update_begin();
 
         if (cpu_hotplug_disabled) {
                 err = -EBUSY;
                 goto out;
         }
         if (!cpu_bootable(cpu)) {
                 err = -EPERM;
                 goto out;
         }
 
         err = _cpu_up(cpu, 0, target);
 out:
         cpu_maps_update_done();
         return err;
 }
 
 /**
  * cpu_device_up - Bring up a cpu device
  * @dev: Pointer to the cpu device to online
  *
  * This function is meant to be used by device core cpu subsystem only.
  *
  * Other subsystems should use add_cpu() instead.
  *
  * Return: %0 on success or a negative errno code
  */
 int cpu_device_up(struct device *dev)
 {
         return cpu_up(dev->id, CPUHP_ONLINE);
 }
 
 int add_cpu(unsigned int cpu)
 {
         int ret;
 
         lock_device_hotplug();
         ret = device_online(get_cpu_device(cpu));
         unlock_device_hotplug();
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(add_cpu);
 
 /**
  * bringup_hibernate_cpu - Bring up the CPU that we hibernated on
  * @sleep_cpu: The cpu we hibernated on and should be brought up.
  *
  * On some architectures like arm64, we can hibernate on any CPU, but on
  * wake up the CPU we hibernated on might be offline as a side effect of
  * using maxcpus= for example.
  *
  * Return: %0 on success or a negative errno code
  */
 int bringup_hibernate_cpu(unsigned int sleep_cpu)
 {
         int ret;
 
         if (!cpu_online(sleep_cpu)) {
                 pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
                 ret = cpu_up(sleep_cpu, CPUHP_ONLINE);
                 if (ret) {
                         pr_err("Failed to bring hibernate-CPU up!\n");
                         return ret;
                 }
         }
         return 0;
 }
 
 static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int ncpus,
                                       enum cpuhp_state target)
 {
         unsigned int cpu;
 
         for_each_cpu(cpu, mask) {
                 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 
                 if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
                         /*
                          * If this failed then cpu_up() might have only
                          * rolled back to CPUHP_BP_KICK_AP for the final
                          * online. Clean it up. NOOP if already rolled back.
                          */
                         WARN_ON(cpuhp_invoke_callback_range(false, cpu, st, CPUHP_OFFLINE));
                 }
 
                 if (!--ncpus)
                         break;
         }
 }
 
 #ifdef CONFIG_HOTPLUG_PARALLEL
 static bool __cpuhp_parallel_bringup __ro_after_init = true;
 
 static int __init parallel_bringup_parse_param(char *arg)
 {
         return kstrtobool(arg, &__cpuhp_parallel_bringup);
 }
 early_param("cpuhp.parallel", parallel_bringup_parse_param);
 
 static inline bool cpuhp_smt_aware(void)
 {
         return cpu_smt_max_threads > 1;
 }
 
 static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
 {
         return cpu_primary_thread_mask;
 }
 
 /*
  * On architectures which have enabled parallel bringup this invokes all BP
  * prepare states for each of the to be onlined APs first. The last state
  * sends the startup IPI to the APs. The APs proceed through the low level
  * bringup code in parallel and then wait for the control CPU to release
  * them one by one for the final onlining procedure.
  *
  * This avoids waiting for each AP to respond to the startup IPI in
  * CPUHP_BRINGUP_CPU.
  */
 static bool __init cpuhp_bringup_cpus_parallel(unsigned int ncpus)
 {
         const struct cpumask *mask = cpu_present_mask;
 
         if (__cpuhp_parallel_bringup)
                 __cpuhp_parallel_bringup = arch_cpuhp_init_parallel_bringup();
         if (!__cpuhp_parallel_bringup)
                 return false;
 
         if (cpuhp_smt_aware()) {
                 const struct cpumask *pmask = cpuhp_get_primary_thread_mask();
                 static struct cpumask tmp_mask __initdata;
 
                 /*
                  * X86 requires to prevent that SMT siblings stopped while
                  * the primary thread does a microcode update for various
                  * reasons. Bring the primary threads up first.
                  */
                 cpumask_and(&tmp_mask, mask, pmask);
                 cpuhp_bringup_mask(&tmp_mask, ncpus, CPUHP_BP_KICK_AP);
                 cpuhp_bringup_mask(&tmp_mask, ncpus, CPUHP_ONLINE);
                 /* Account for the online CPUs */
                 ncpus -= num_online_cpus();
                 if (!ncpus)
                         return true;
                 /* Create the mask for secondary CPUs */
                 cpumask_andnot(&tmp_mask, mask, pmask);
                 mask = &tmp_mask;
         }
 
         /* Bring the not-yet started CPUs up */
         cpuhp_bringup_mask(mask, ncpus, CPUHP_BP_KICK_AP);
         cpuhp_bringup_mask(mask, ncpus, CPUHP_ONLINE);
         return true;
 }
 #else
 static inline bool cpuhp_bringup_cpus_parallel(unsigned int ncpus) { return false; }
 #endif /* CONFIG_HOTPLUG_PARALLEL */
 
 void __init bringup_nonboot_cpus(unsigned int max_cpus)
 {
         if (!max_cpus)
                 return;
 
         /* Try parallel bringup optimization if enabled */
         if (cpuhp_bringup_cpus_parallel(max_cpus))
                 return;
 
         /* Full per CPU serialized bringup */
         cpuhp_bringup_mask(cpu_present_mask, max_cpus, CPUHP_ONLINE);
 }
 
 #ifdef CONFIG_PM_SLEEP_SMP
 static cpumask_var_t frozen_cpus;
 
 int freeze_secondary_cpus(int primary)
 {
         int cpu, error = 0;
 
         cpu_maps_update_begin();
         if (primary == -1) {
                 primary = cpumask_first(cpu_online_mask);
                 if (!housekeeping_cpu(primary, HK_TYPE_TIMER))
                         primary = housekeeping_any_cpu(HK_TYPE_TIMER);
         } else {
                 if (!cpu_online(primary))
                         primary = cpumask_first(cpu_online_mask);
         }
 
         /*
          * We take down all of the non-boot CPUs in one shot to avoid races
          * with the userspace trying to use the CPU hotplug at the same time
          */
         cpumask_clear(frozen_cpus);
 
         pr_info("Disabling non-boot CPUs ...\n");
         for (cpu = nr_cpu_ids - 1; cpu >= 0; cpu--) {
                 if (!cpu_online(cpu) || cpu == primary)
                         continue;
 
                 if (pm_wakeup_pending()) {
                         pr_info("Wakeup pending. Abort CPU freeze\n");
                         error = -EBUSY;
                         break;
                 }
 
                 trace_suspend_resume(TPS("CPU_OFF"), cpu, true);
                 error = _cpu_down(cpu, 1, CPUHP_OFFLINE);
                 trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
                 if (!error)
                         cpumask_set_cpu(cpu, frozen_cpus);
                 else {
                         pr_err("Error taking CPU%d down: %d\n", cpu, error);
                         break;
                 }
         }
 
         if (!error)
                 BUG_ON(num_online_cpus() > 1);
         else
                 pr_err("Non-boot CPUs are not disabled\n");
 
         /*
          * Make sure the CPUs won't be enabled by someone else. We need to do
          * this even in case of failure as all freeze_secondary_cpus() users are
          * supposed to do thaw_secondary_cpus() on the failure path.
          */
         cpu_hotplug_disabled++;
 
         cpu_maps_update_done();
         return error;
 }
 
 void __weak arch_thaw_secondary_cpus_begin(void)
 {
 }
 
 void __weak arch_thaw_secondary_cpus_end(void)
 {
 }
 
 void thaw_secondary_cpus(void)
 {
         int cpu, error;
 
         /* Allow everyone to use the CPU hotplug again */
         cpu_maps_update_begin();
         __cpu_hotplug_enable();
         if (cpumask_empty(frozen_cpus))
                 goto out;
 
         pr_info("Enabling non-boot CPUs ...\n");
 
         arch_thaw_secondary_cpus_begin();
 
         for_each_cpu(cpu, frozen_cpus) {
                 trace_suspend_resume(TPS("CPU_ON"), cpu, true);
                 error = _cpu_up(cpu, 1, CPUHP_ONLINE);
                 trace_suspend_resume(TPS("CPU_ON"), cpu, false);
                 if (!error) {
                         pr_info("CPU%d is up\n", cpu);
                         continue;
                 }
                 pr_warn("Error taking CPU%d up: %d\n", cpu, error);
         }
 
         arch_thaw_secondary_cpus_end();
 
         cpumask_clear(frozen_cpus);
 out:
         cpu_maps_update_done();
 }
 
 static int __init alloc_frozen_cpus(void)
 {
         if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
                 return -ENOMEM;
         return 0;
 }
 core_initcall(alloc_frozen_cpus);
 
 /*
  * When callbacks for CPU hotplug notifications are being executed, we must
  * ensure that the state of the system with respect to the tasks being frozen
  * or not, as reported by the notification, remains unchanged *throughout the
  * duration* of the execution of the callbacks.
  * Hence we need to prevent the freezer from racing with regular CPU hotplug.
  *
  * This synchronization is implemented by mutually excluding regular CPU
  * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
  * Hibernate notifications.
  */
 static int
 cpu_hotplug_pm_callback(struct notifier_block *nb,
                         unsigned long action, void *ptr)
 {
         switch (action) {
 
         case PM_SUSPEND_PREPARE:
         case PM_HIBERNATION_PREPARE:
                 cpu_hotplug_disable();
                 break;
 
         case PM_POST_SUSPEND:
         case PM_POST_HIBERNATION:
                 cpu_hotplug_enable();
                 break;
 
         default:
                 return NOTIFY_DONE;
         }
 
         return NOTIFY_OK;
 }
 
 
 static int __init cpu_hotplug_pm_sync_init(void)
 {
         /*
          * cpu_hotplug_pm_callback has higher priority than x86
          * bsp_pm_callback which depends on cpu_hotplug_pm_callback
          * to disable cpu hotplug to avoid cpu hotplug race.
          */
         pm_notifier(cpu_hotplug_pm_callback, 0);
         return 0;
 }
 core_initcall(cpu_hotplug_pm_sync_init);
 
 #endif /* CONFIG_PM_SLEEP_SMP */
 
 int __boot_cpu_id;
 
 #endif /* CONFIG_SMP */
 
 /* Boot processor state steps */
 static struct cpuhp_step cpuhp_hp_states[] = {
         [CPUHP_OFFLINE] = {
                 .name                   = "offline",
                 .startup.single         = NULL,
                 .teardown.single        = NULL,
         },
 #ifdef CONFIG_SMP
         [CPUHP_CREATE_THREADS]= {
                 .name                   = "threads:prepare",
                 .startup.single         = smpboot_create_threads,
                 .teardown.single        = NULL,
                 .cant_stop              = true,
         },
         [CPUHP_PERF_PREPARE] = {
                 .name                   = "perf:prepare",
                 .startup.single         = perf_event_init_cpu,
                 .teardown.single        = perf_event_exit_cpu,
         },
         [CPUHP_RANDOM_PREPARE] = {
                 .name                   = "random:prepare",
                 .startup.single         = random_prepare_cpu,
                 .teardown.single        = NULL,
         },
         [CPUHP_WORKQUEUE_PREP] = {
                 .name                   = "workqueue:prepare",
                 .startup.single         = workqueue_prepare_cpu,
                 .teardown.single        = NULL,
         },
         [CPUHP_HRTIMERS_PREPARE] = {
                 .name                   = "hrtimers:prepare",
                 .startup.single         = hrtimers_prepare_cpu,
                 .teardown.single        = NULL,
         },
         [CPUHP_SMPCFD_PREPARE] = {
                 .name                   = "smpcfd:prepare",
                 .startup.single         = smpcfd_prepare_cpu,
                 .teardown.single        = smpcfd_dead_cpu,
         },
         [CPUHP_RELAY_PREPARE] = {
                 .name                   = "relay:prepare",
                 .startup.single         = relay_prepare_cpu,
                 .teardown.single        = NULL,
         },
         [CPUHP_RCUTREE_PREP] = {
                 .name                   = "RCU/tree:prepare",
                 .startup.single         = rcutree_prepare_cpu,
                 .teardown.single        = rcutree_dead_cpu,
         },
         /*
          * On the tear-down path, timers_dead_cpu() must be invoked
          * before blk_mq_queue_reinit_notify() from notify_dead(),
          * otherwise a RCU stall occurs.
          */
         [CPUHP_TIMERS_PREPARE] = {
                 .name                   = "timers:prepare",
                 .startup.single         = timers_prepare_cpu,
                 .teardown.single        = timers_dead_cpu,
         },
 
 #ifdef CONFIG_HOTPLUG_SPLIT_STARTUP
         /*
          * Kicks the AP alive. AP will wait in cpuhp_ap_sync_alive() until
          * the next step will release it.
          */
         [CPUHP_BP_KICK_AP] = {
                 .name                   = "cpu:kick_ap",
                 .startup.single         = cpuhp_kick_ap_alive,
         },
 
         /*
          * Waits for the AP to reach cpuhp_ap_sync_alive() and then
          * releases it for the complete bringup.
          */
         [CPUHP_BRINGUP_CPU] = {
                 .name                   = "cpu:bringup",
                 .startup.single         = cpuhp_bringup_ap,
                 .teardown.single        = finish_cpu,
                 .cant_stop              = true,
         },
 #else
         /*
          * All-in-one CPU bringup state which includes the kick alive.
          */
         [CPUHP_BRINGUP_CPU] = {
                 .name                   = "cpu:bringup",
                 .startup.single         = bringup_cpu,
                 .teardown.single        = finish_cpu,
                 .cant_stop              = true,
         },
 #endif
         /* Final state before CPU kills itself */
         [CPUHP_AP_IDLE_DEAD] = {
                 .name                   = "idle:dead",
         },
         /*
          * Last state before CPU enters the idle loop to die. Transient state
          * for synchronization.
          */
         [CPUHP_AP_OFFLINE] = {
                 .name                   = "ap:offline",
                 .cant_stop              = true,
         },
         /* First state is scheduler control. Interrupts are disabled */
         [CPUHP_AP_SCHED_STARTING] = {
                 .name                   = "sched:starting",
                 .startup.single         = sched_cpu_starting,
                 .teardown.single        = sched_cpu_dying,
         },
         [CPUHP_AP_RCUTREE_DYING] = {
                 .name                   = "RCU/tree:dying",
                 .startup.single         = NULL,
                 .teardown.single        = rcutree_dying_cpu,
         },
         [CPUHP_AP_SMPCFD_DYING] = {
                 .name                   = "smpcfd:dying",
                 .startup.single         = NULL,
                 .teardown.single        = smpcfd_dying_cpu,
         },
         [CPUHP_AP_HRTIMERS_DYING] = {
                 .name                   = "hrtimers:dying",
                 .startup.single         = NULL,
                 .teardown.single        = hrtimers_cpu_dying,
         },
         [CPUHP_AP_TICK_DYING] = {
                 .name                   = "tick:dying",
                 .startup.single         = NULL,
                 .teardown.single        = tick_cpu_dying,
         },
         /* Entry state on starting. Interrupts enabled from here on. Transient
          * state for synchronsization */
         [CPUHP_AP_ONLINE] = {
                 .name                   = "ap:online",
         },
         /*
          * Handled on control processor until the plugged processor manages
          * this itself.
          */
         [CPUHP_TEARDOWN_CPU] = {
                 .name                   = "cpu:teardown",
                 .startup.single         = NULL,
                 .teardown.single        = takedown_cpu,
                 .cant_stop              = true,
         },
 
         [CPUHP_AP_SCHED_WAIT_EMPTY] = {
                 .name                   = "sched:waitempty",
                 .startup.single         = NULL,
                 .teardown.single        = sched_cpu_wait_empty,
         },
 
         /* Handle smpboot threads park/unpark */
         [CPUHP_AP_SMPBOOT_THREADS] = {
                 .name                   = "smpboot/threads:online",
                 .startup.single         = smpboot_unpark_threads,
                 .teardown.single        = smpboot_park_threads,
         },
         [CPUHP_AP_IRQ_AFFINITY_ONLINE] = {
                 .name                   = "irq/affinity:online",
                 .startup.single         = irq_affinity_online_cpu,
                 .teardown.single        = NULL,
         },
         [CPUHP_AP_PERF_ONLINE] = {
                 .name                   = "perf:online",
                 .startup.single         = perf_event_init_cpu,
                 .teardown.single        = perf_event_exit_cpu,
         },
         [CPUHP_AP_WATCHDOG_ONLINE] = {
                 .name                   = "lockup_detector:online",
                 .startup.single         = lockup_detector_online_cpu,
                 .teardown.single        = lockup_detector_offline_cpu,
         },
         [CPUHP_AP_WORKQUEUE_ONLINE] = {
                 .name                   = "workqueue:online",
                 .startup.single         = workqueue_online_cpu,
                 .teardown.single        = workqueue_offline_cpu,
         },
         [CPUHP_AP_RANDOM_ONLINE] = {
                 .name                   = "random:online",
                 .startup.single         = random_online_cpu,
                 .teardown.single        = NULL,
         },
         [CPUHP_AP_RCUTREE_ONLINE] = {
                 .name                   = "RCU/tree:online",
                 .startup.single         = rcutree_online_cpu,
                 .teardown.single        = rcutree_offline_cpu,
         },
 #endif
         /*
          * The dynamically registered state space is here
          */
 
 #ifdef CONFIG_SMP
         /* Last state is scheduler control setting the cpu active */
         [CPUHP_AP_ACTIVE] = {
                 .name                   = "sched:active",
                 .startup.single         = sched_cpu_activate,
                 .teardown.single        = sched_cpu_deactivate,
         },
 #endif
 
         /* CPU is fully up and running. */
         [CPUHP_ONLINE] = {
                 .name                   = "online",
                 .startup.single         = NULL,
                 .teardown.single        = NULL,
         },
 };
 
 /* Sanity check for callbacks */
 static int cpuhp_cb_check(enum cpuhp_state state)
 {
         if (state <= CPUHP_OFFLINE || state >= CPUHP_ONLINE)
                 return -EINVAL;
         return 0;
 }
 
 /*
  * Returns a free for dynamic slot assignment of the Online state. The states
  * are protected by the cpuhp_slot_states mutex and an empty slot is identified
  * by having no name assigned.
  */
 static int cpuhp_reserve_state(enum cpuhp_state state)
 {
         enum cpuhp_state i, end;
         struct cpuhp_step *step;
 
         switch (state) {
         case CPUHP_AP_ONLINE_DYN:
                 step = cpuhp_hp_states + CPUHP_AP_ONLINE_DYN;
                 end = CPUHP_AP_ONLINE_DYN_END;
                 break;
         case CPUHP_BP_PREPARE_DYN:
                 step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN;
                 end = CPUHP_BP_PREPARE_DYN_END;
                 break;
         default:
                 return -EINVAL;
         }
 
         for (i = state; i <= end; i++, step++) {
                 if (!step->name)
                         return i;
         }
         WARN(1, "No more dynamic states available for CPU hotplug\n");
         return -ENOSPC;
 }
 
 static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
                                  int (*startup)(unsigned int cpu),
                                  int (*teardown)(unsigned int cpu),
                                  bool multi_instance)
 {
         /* (Un)Install the callbacks for further cpu hotplug operations */
         struct cpuhp_step *sp;
         int ret = 0;
 
         /*
          * If name is NULL, then the state gets removed.
          *
          * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
          * the first allocation from these dynamic ranges, so the removal
          * would trigger a new allocation and clear the wrong (already
          * empty) state, leaving the callbacks of the to be cleared state
          * dangling, which causes wreckage on the next hotplug operation.
          */
         if (name && (state == CPUHP_AP_ONLINE_DYN ||
                      state == CPUHP_BP_PREPARE_DYN)) {
                 ret = cpuhp_reserve_state(state);
                 if (ret < 0)
                         return ret;
                 state = ret;
         }
         sp = cpuhp_get_step(state);
         if (name && sp->name)
                 return -EBUSY;
 
         sp->startup.single = startup;
         sp->teardown.single = teardown;
         sp->name = name;
         sp->multi_instance = multi_instance;
         INIT_HLIST_HEAD(&sp->list);
         return ret;
 }
 
 static void *cpuhp_get_teardown_cb(enum cpuhp_state state)
 {
         return cpuhp_get_step(state)->teardown.single;
 }
 
 /*
  * Call the startup/teardown function for a step either on the AP or
  * on the current CPU.
  */
 static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
                             struct hlist_node *node)
 {
         struct cpuhp_step *sp = cpuhp_get_step(state);
         int ret;
 
         /*
          * If there's nothing to do, we done.
          * Relies on the union for multi_instance.
          */
         if (cpuhp_step_empty(bringup, sp))
                 return 0;
         /*
          * The non AP bound callbacks can fail on bringup. On teardown
          * e.g. module removal we crash for now.
          */
 #ifdef CONFIG_SMP
         if (cpuhp_is_ap_state(state))
                 ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
         else
                 ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
 #else
         ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
 #endif
         BUG_ON(ret && !bringup);
         return ret;
 }
 
 /*
  * Called from __cpuhp_setup_state on a recoverable failure.
  *
  * Note: The teardown callbacks for rollback are not allowed to fail!
  */
 static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state,
                                    struct hlist_node *node)
 {
         int cpu;
 
         /* Roll back the already executed steps on the other cpus */
         for_each_present_cpu(cpu) {
                 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                 int cpustate = st->state;
 
                 if (cpu >= failedcpu)
                         break;
 
                 /* Did we invoke the startup call on that cpu ? */
                 if (cpustate >= state)
                         cpuhp_issue_call(cpu, state, false, node);
         }
 }
 
 int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
                                           struct hlist_node *node,
                                           bool invoke)
 {
         struct cpuhp_step *sp;
         int cpu;
         int ret;
 
         lockdep_assert_cpus_held();
 
         sp = cpuhp_get_step(state);
         if (sp->multi_instance == false)
                 return -EINVAL;
 
         mutex_lock(&cpuhp_state_mutex);
 
         if (!invoke || !sp->startup.multi)
                 goto add_node;
 
         /*
          * Try to call the startup callback for each present cpu
          * depending on the hotplug state of the cpu.
          */
         for_each_present_cpu(cpu) {
                 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                 int cpustate = st->state;
 
                 if (cpustate < state)
                         continue;
 
                 ret = cpuhp_issue_call(cpu, state, true, node);
                 if (ret) {
                         if (sp->teardown.multi)
                                 cpuhp_rollback_install(cpu, state, node);
                         goto unlock;
                 }
         }
 add_node:
         ret = 0;
         hlist_add_head(node, &sp->list);
 unlock:
         mutex_unlock(&cpuhp_state_mutex);
         return ret;
 }
 
 int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
                                bool invoke)
 {
         int ret;
 
         cpus_read_lock();
         ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
         cpus_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
 
 /**
  * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
  * @state:              The state to setup
  * @name:               Name of the step
  * @invoke:             If true, the startup function is invoked for cpus where
  *                      cpu state >= @state
  * @startup:            startup callback function
  * @teardown:           teardown callback function
  * @multi_instance:     State is set up for multiple instances which get
  *                      added afterwards.
  *
  * The caller needs to hold cpus read locked while calling this function.
  * Return:
  *   On success:
  *      Positive state number if @state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN;
  *      0 for all other states
  *   On failure: proper (negative) error code
  */
 int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
                                    const char *name, bool invoke,
                                    int (*startup)(unsigned int cpu),
                                    int (*teardown)(unsigned int cpu),
                                    bool multi_instance)
 {
         int cpu, ret = 0;
         bool dynstate;
 
         lockdep_assert_cpus_held();
 
         if (cpuhp_cb_check(state) || !name)
                 return -EINVAL;
 
         mutex_lock(&cpuhp_state_mutex);
 
         ret = cpuhp_store_callbacks(state, name, startup, teardown,
                                     multi_instance);
 
         dynstate = state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN;
         if (ret > 0 && dynstate) {
                 state = ret;
                 ret = 0;
         }
 
         if (ret || !invoke || !startup)
                 goto out;
 
         /*
          * Try to call the startup callback for each present cpu
          * depending on the hotplug state of the cpu.
          */
         for_each_present_cpu(cpu) {
                 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                 int cpustate = st->state;
 
                 if (cpustate < state)
                         continue;
 
                 ret = cpuhp_issue_call(cpu, state, true, NULL);
                 if (ret) {
                         if (teardown)
                                 cpuhp_rollback_install(cpu, state, NULL);
                         cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
                         goto out;
                 }
         }
 out:
         mutex_unlock(&cpuhp_state_mutex);
         /*
          * If the requested state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN,
          * return the dynamically allocated state in case of success.
          */
         if (!ret && dynstate)
                 return state;
         return ret;
 }
 EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);
 
 int __cpuhp_setup_state(enum cpuhp_state state,
                         const char *name, bool invoke,
                         int (*startup)(unsigned int cpu),
                         int (*teardown)(unsigned int cpu),
                         bool multi_instance)
 {
         int ret;
 
         cpus_read_lock();
         ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup,
                                              teardown, multi_instance);
         cpus_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL(__cpuhp_setup_state);
 
 int __cpuhp_state_remove_instance(enum cpuhp_state state,
                                   struct hlist_node *node, bool invoke)
 {
         struct cpuhp_step *sp = cpuhp_get_step(state);
         int cpu;
 
         BUG_ON(cpuhp_cb_check(state));
 
         if (!sp->multi_instance)
                 return -EINVAL;
 
         cpus_read_lock();
         mutex_lock(&cpuhp_state_mutex);
 
         if (!invoke || !cpuhp_get_teardown_cb(state))
                 goto remove;
         /*
          * Call the teardown callback for each present cpu depending
          * on the hotplug state of the cpu. This function is not
          * allowed to fail currently!
          */
         for_each_present_cpu(cpu) {
                 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                 int cpustate = st->state;
 
                 if (cpustate >= state)
                         cpuhp_issue_call(cpu, state, false, node);
         }
 
 remove:
         hlist_del(node);
         mutex_unlock(&cpuhp_state_mutex);
         cpus_read_unlock();
 
         return 0;
 }
 EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);
 
 /**
  * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
  * @state:      The state to remove
  * @invoke:     If true, the teardown function is invoked for cpus where
  *              cpu state >= @state
  *
  * The caller needs to hold cpus read locked while calling this function.
  * The teardown callback is currently not allowed to fail. Think
  * about module removal!
  */
 void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
 {
         struct cpuhp_step *sp = cpuhp_get_step(state);
         int cpu;
 
         BUG_ON(cpuhp_cb_check(state));
 
         lockdep_assert_cpus_held();
 
         mutex_lock(&cpuhp_state_mutex);
         if (sp->multi_instance) {
                 WARN(!hlist_empty(&sp->list),
                      "Error: Removing state %d which has instances left.\n",
                      state);
                 goto remove;
         }
 
         if (!invoke || !cpuhp_get_teardown_cb(state))
                 goto remove;
 
         /*
          * Call the teardown callback for each present cpu depending
          * on the hotplug state of the cpu. This function is not
          * allowed to fail currently!
          */
         for_each_present_cpu(cpu) {
                 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                 int cpustate = st->state;
 
                 if (cpustate >= state)
                         cpuhp_issue_call(cpu, state, false, NULL);
         }
 remove:
         cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
         mutex_unlock(&cpuhp_state_mutex);
 }
 EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);
 
 void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
 {
         cpus_read_lock();
         __cpuhp_remove_state_cpuslocked(state, invoke);
         cpus_read_unlock();
 }
 EXPORT_SYMBOL(__cpuhp_remove_state);
 
 #ifdef CONFIG_HOTPLUG_SMT
 static void cpuhp_offline_cpu_device(unsigned int cpu)
 {
         struct device *dev = get_cpu_device(cpu);
 
         dev->offline = true;
         /* Tell user space about the state change */
         kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
 }
 
 static void cpuhp_online_cpu_device(unsigned int cpu)
 {
         struct device *dev = get_cpu_device(cpu);
 
         dev->offline = false;
         /* Tell user space about the state change */
         kobject_uevent(&dev->kobj, KOBJ_ONLINE);
 }
 
 int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 {
         int cpu, ret = 0;
 
         cpu_maps_update_begin();
         for_each_online_cpu(cpu) {
                 if (topology_is_primary_thread(cpu))
                         continue;
                 /*
                  * Disable can be called with CPU_SMT_ENABLED when changing
                  * from a higher to lower number of SMT threads per core.
                  */
                 if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
                         continue;
                 ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
                 if (ret)
                         break;
                 /*
                  * As this needs to hold the cpu maps lock it's impossible
                  * to call device_offline() because that ends up calling
                  * cpu_down() which takes cpu maps lock. cpu maps lock
                  * needs to be held as this might race against in kernel
                  * abusers of the hotplug machinery (thermal management).
                  *
                  * So nothing would update device:offline state. That would
                  * leave the sysfs entry stale and prevent onlining after
                  * smt control has been changed to 'off' again. This is
                  * called under the sysfs hotplug lock, so it is properly
                  * serialized against the regular offline usage.
                  */
                 cpuhp_offline_cpu_device(cpu);
         }
         if (!ret)
                 cpu_smt_control = ctrlval;
         cpu_maps_update_done();
         return ret;
 }
 
 /**
  * Check if the core a CPU belongs to is online
  */
 #if !defined(topology_is_core_online)
 static inline bool topology_is_core_online(unsigned int cpu)
 {
         return true;
 }
 #endif
 
 int cpuhp_smt_enable(void)
 {
         int cpu, ret = 0;
 
         cpu_maps_update_begin();
         cpu_smt_control = CPU_SMT_ENABLED;
         for_each_present_cpu(cpu) {
                 /* Skip online CPUs and CPUs on offline nodes */
                 if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
                         continue;
                 if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu))
                         continue;
                 ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
                 if (ret)
                         break;
                 /* See comment in cpuhp_smt_disable() */
                 cpuhp_online_cpu_device(cpu);
         }
         cpu_maps_update_done();
         return ret;
 }
 #endif
 
 #if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
 static ssize_t state_show(struct device *dev,
                           struct device_attribute *attr, char *buf)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
         return sprintf(buf, "%d\n", st->state);
 }
 static DEVICE_ATTR_RO(state);
 
 static ssize_t target_store(struct device *dev, struct device_attribute *attr,
                             const char *buf, size_t count)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
         struct cpuhp_step *sp;
         int target, ret;
 
         ret = kstrtoint(buf, 10, &target);
         if (ret)
                 return ret;
 
 #ifdef CONFIG_CPU_HOTPLUG_STATE_CONTROL
         if (target < CPUHP_OFFLINE || target > CPUHP_ONLINE)
                 return -EINVAL;
 #else
         if (target != CPUHP_OFFLINE && target != CPUHP_ONLINE)
                 return -EINVAL;
 #endif
 
         ret = lock_device_hotplug_sysfs();
         if (ret)
                 return ret;
 
         mutex_lock(&cpuhp_state_mutex);
         sp = cpuhp_get_step(target);
         ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
         mutex_unlock(&cpuhp_state_mutex);
         if (ret)
                 goto out;
 
         if (st->state < target)
                 ret = cpu_up(dev->id, target);
         else if (st->state > target)
                 ret = cpu_down(dev->id, target);
         else if (WARN_ON(st->target != target))
                 st->target = target;
 out:
         unlock_device_hotplug();
         return ret ? ret : count;
 }
 
 static ssize_t target_show(struct device *dev,
                            struct device_attribute *attr, char *buf)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
         return sprintf(buf, "%d\n", st->target);
 }
 static DEVICE_ATTR_RW(target);
 
 static ssize_t fail_store(struct device *dev, struct device_attribute *attr,
                           const char *buf, size_t count)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
         struct cpuhp_step *sp;
         int fail, ret;
 
         ret = kstrtoint(buf, 10, &fail);
         if (ret)
                 return ret;
 
         if (fail == CPUHP_INVALID) {
                 st->fail = fail;
                 return count;
         }
 
         if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE)
                 return -EINVAL;
 
         /*
          * Cannot fail STARTING/DYING callbacks.
          */
         if (cpuhp_is_atomic_state(fail))
                 return -EINVAL;
 
         /*
          * DEAD callbacks cannot fail...
          * ... neither can CPUHP_BRINGUP_CPU during hotunplug. The latter
          * triggering STARTING callbacks, a failure in this state would
          * hinder rollback.
          */
         if (fail <= CPUHP_BRINGUP_CPU && st->state > CPUHP_BRINGUP_CPU)
                 return -EINVAL;
 
         /*
          * Cannot fail anything that doesn't have callbacks.
          */
         mutex_lock(&cpuhp_state_mutex);
         sp = cpuhp_get_step(fail);
         if (!sp->startup.single && !sp->teardown.single)
                 ret = -EINVAL;
         mutex_unlock(&cpuhp_state_mutex);
         if (ret)
                 return ret;
 
         st->fail = fail;
 
         return count;
 }
 
 static ssize_t fail_show(struct device *dev,
                          struct device_attribute *attr, char *buf)
 {
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
         return sprintf(buf, "%d\n", st->fail);
 }
 
 static DEVICE_ATTR_RW(fail);
 
 static struct attribute *cpuhp_cpu_attrs[] = {
         &dev_attr_state.attr,
         &dev_attr_target.attr,
         &dev_attr_fail.attr,
         NULL
 };
 
 static const struct attribute_group cpuhp_cpu_attr_group = {
         .attrs = cpuhp_cpu_attrs,
         .name = "hotplug",
         NULL
 };
 
 static ssize_t states_show(struct device *dev,
                                  struct device_attribute *attr, char *buf)
 {
         ssize_t cur, res = 0;
         int i;
 
         mutex_lock(&cpuhp_state_mutex);
         for (i = CPUHP_OFFLINE; i <= CPUHP_ONLINE; i++) {
                 struct cpuhp_step *sp = cpuhp_get_step(i);
 
                 if (sp->name) {
                         cur = sprintf(buf, "%3d: %s\n", i, sp->name);
                         buf += cur;
                         res += cur;
                 }
         }
         mutex_unlock(&cpuhp_state_mutex);
         return res;
 }
 static DEVICE_ATTR_RO(states);
 
 static struct attribute *cpuhp_cpu_root_attrs[] = {
         &dev_attr_states.attr,
         NULL
 };
 
 static const struct attribute_group cpuhp_cpu_root_attr_group = {
         .attrs = cpuhp_cpu_root_attrs,
         .name = "hotplug",
         NULL
 };
 
 #ifdef CONFIG_HOTPLUG_SMT
 
 static bool cpu_smt_num_threads_valid(unsigned int threads)
 {
         if (IS_ENABLED(CONFIG_SMT_NUM_THREADS_DYNAMIC))
                 return threads >= 1 && threads <= cpu_smt_max_threads;
         return threads == 1 || threads == cpu_smt_max_threads;
 }
 
 static ssize_t
 __store_smt_control(struct device *dev, struct device_attribute *attr,
                     const char *buf, size_t count)
 {
         int ctrlval, ret, num_threads, orig_threads;
         bool force_off;
 
         if (cpu_smt_control == CPU_SMT_FORCE_DISABLED)
                 return -EPERM;
 
         if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
                 return -ENODEV;
 
         if (sysfs_streq(buf, "on")) {
                 ctrlval = CPU_SMT_ENABLED;
                 num_threads = cpu_smt_max_threads;
         } else if (sysfs_streq(buf, "off")) {
                 ctrlval = CPU_SMT_DISABLED;
                 num_threads = 1;
         } else if (sysfs_streq(buf, "forceoff")) {
                 ctrlval = CPU_SMT_FORCE_DISABLED;
                 num_threads = 1;
         } else if (kstrtoint(buf, 10, &num_threads) == 0) {
                 if (num_threads == 1)
                         ctrlval = CPU_SMT_DISABLED;
                 else if (cpu_smt_num_threads_valid(num_threads))
                         ctrlval = CPU_SMT_ENABLED;
                 else
                         return -EINVAL;
         } else {
                 return -EINVAL;
         }
 
         ret = lock_device_hotplug_sysfs();
         if (ret)
                 return ret;
 
         orig_threads = cpu_smt_num_threads;
         cpu_smt_num_threads = num_threads;
 
         force_off = ctrlval != cpu_smt_control && ctrlval == CPU_SMT_FORCE_DISABLED;
 
         if (num_threads > orig_threads)
                 ret = cpuhp_smt_enable();
         else if (num_threads < orig_threads || force_off)
                 ret = cpuhp_smt_disable(ctrlval);
 
         unlock_device_hotplug();
         return ret ? ret : count;
 }
 
 #else /* !CONFIG_HOTPLUG_SMT */
 static ssize_t
 __store_smt_control(struct device *dev, struct device_attribute *attr,
                     const char *buf, size_t count)
 {
         return -ENODEV;
 }
 #endif /* CONFIG_HOTPLUG_SMT */
 
 static const char *smt_states[] = {
         [CPU_SMT_ENABLED]               = "on",
         [CPU_SMT_DISABLED]              = "off",
         [CPU_SMT_FORCE_DISABLED]        = "forceoff",
         [CPU_SMT_NOT_SUPPORTED]         = "notsupported",
         [CPU_SMT_NOT_IMPLEMENTED]       = "notimplemented",
 };
 
 static ssize_t control_show(struct device *dev,
                             struct device_attribute *attr, char *buf)
 {
         const char *state = smt_states[cpu_smt_control];
 
 #ifdef CONFIG_HOTPLUG_SMT
         /*
          * If SMT is enabled but not all threads are enabled then show the
          * number of threads. If all threads are enabled show "on". Otherwise
          * show the state name.
          */
         if (cpu_smt_control == CPU_SMT_ENABLED &&
             cpu_smt_num_threads != cpu_smt_max_threads)
                 return sysfs_emit(buf, "%d\n", cpu_smt_num_threads);
 #endif
 
         return sysfs_emit(buf, "%s\n", state);
 }
 
 static ssize_t control_store(struct device *dev, struct device_attribute *attr,
                              const char *buf, size_t count)
 {
         return __store_smt_control(dev, attr, buf, count);
 }
 static DEVICE_ATTR_RW(control);
 
 static ssize_t active_show(struct device *dev,
                            struct device_attribute *attr, char *buf)
 {
         return sysfs_emit(buf, "%d\n", sched_smt_active());
 }
 static DEVICE_ATTR_RO(active);
 
 static struct attribute *cpuhp_smt_attrs[] = {
         &dev_attr_control.attr,
         &dev_attr_active.attr,
         NULL
 };
 
 static const struct attribute_group cpuhp_smt_attr_group = {
         .attrs = cpuhp_smt_attrs,
         .name = "smt",
         NULL
 };
 
 static int __init cpu_smt_sysfs_init(void)
 {
         struct device *dev_root;
         int ret = -ENODEV;
 
         dev_root = bus_get_dev_root(&cpu_subsys);
         if (dev_root) {
                 ret = sysfs_create_group(&dev_root->kobj, &cpuhp_smt_attr_group);
                 put_device(dev_root);
         }
         return ret;
 }
 
 static int __init cpuhp_sysfs_init(void)
 {
         struct device *dev_root;
         int cpu, ret;
 
         ret = cpu_smt_sysfs_init();
         if (ret)
                 return ret;
 
         dev_root = bus_get_dev_root(&cpu_subsys);
         if (dev_root) {
                 ret = sysfs_create_group(&dev_root->kobj, &cpuhp_cpu_root_attr_group);
                 put_device(dev_root);
                 if (ret)
                         return ret;
         }
 
         for_each_possible_cpu(cpu) {
                 struct device *dev = get_cpu_device(cpu);
 
                 if (!dev)
                         continue;
                 ret = sysfs_create_group(&dev->kobj, &cpuhp_cpu_attr_group);
                 if (ret)
                         return ret;
         }
         return 0;
 }
 device_initcall(cpuhp_sysfs_init);
 #endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */
 
 /*
  * cpu_bit_bitmap[] is a special, "compressed" data structure that
  * represents all NR_CPUS bits binary values of 1<<nr.
  *
  * It is used by cpumask_of() to get a constant address to a CPU
  * mask value that has a single bit set only.
  */
 
 /* cpu_bit_bitmap[0] is empty - so we can back into it */
 #define MASK_DECLARE_1(x)       [x+1][0] = (1UL << (x))
 #define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 #define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 #define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 
 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 
         MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
         MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
 #if BITS_PER_LONG > 32
         MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
         MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
 #endif
 };
 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 
 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 EXPORT_SYMBOL(cpu_all_bits);
 
 #ifdef CONFIG_INIT_ALL_POSSIBLE
 struct cpumask __cpu_possible_mask __ro_after_init
         = {CPU_BITS_ALL};
 #else
 struct cpumask __cpu_possible_mask __ro_after_init;
 #endif
 EXPORT_SYMBOL(__cpu_possible_mask);
 
 struct cpumask __cpu_online_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_online_mask);
 
 struct cpumask __cpu_enabled_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_enabled_mask);
 
 struct cpumask __cpu_present_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_present_mask);
 
 struct cpumask __cpu_active_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_active_mask);
 
 struct cpumask __cpu_dying_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_dying_mask);
 
 atomic_t __num_online_cpus __read_mostly;
 EXPORT_SYMBOL(__num_online_cpus);
 
 void init_cpu_present(const struct cpumask *src)
 {
         cpumask_copy(&__cpu_present_mask, src);
 }
 
 void init_cpu_possible(const struct cpumask *src)
 {
         cpumask_copy(&__cpu_possible_mask, src);
 }
 
 void init_cpu_online(const struct cpumask *src)
 {
         cpumask_copy(&__cpu_online_mask, src);
 }
 
 void set_cpu_online(unsigned int cpu, bool online)
 {
         /*
          * atomic_inc/dec() is required to handle the horrid abuse of this
          * function by the reboot and kexec code which invoke it from
          * IPI/NMI broadcasts when shutting down CPUs. Invocation from
          * regular CPU hotplug is properly serialized.
          *
          * Note, that the fact that __num_online_cpus is of type atomic_t
          * does not protect readers which are not serialized against
          * concurrent hotplug operations.
          */
         if (online) {
                 if (!cpumask_test_and_set_cpu(cpu, &__cpu_online_mask))
                         atomic_inc(&__num_online_cpus);
         } else {
                 if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask))
                         atomic_dec(&__num_online_cpus);
         }
 }
 
 /*
  * Activate the first processor.
  */
 void __init boot_cpu_init(void)
 {
         int cpu = smp_processor_id();
 
         /* Mark the boot cpu "present", "online" etc for SMP and UP case */
         set_cpu_online(cpu, true);
         set_cpu_active(cpu, true);
         set_cpu_present(cpu, true);
         set_cpu_possible(cpu, true);
 
 #ifdef CONFIG_SMP
         __boot_cpu_id = cpu;
 #endif
 }
 
 /*
  * Must be called _AFTER_ setting up the per_cpu areas
  */
 void __init boot_cpu_hotplug_init(void)
 {
 #ifdef CONFIG_SMP
         cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
         atomic_set(this_cpu_ptr(&cpuhp_state.ap_sync_state), SYNC_STATE_ONLINE);
 #endif
         this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
         this_cpu_write(cpuhp_state.target, CPUHP_ONLINE);
 }
 
 #ifdef CONFIG_CPU_MITIGATIONS
 /*
  * These are used for a global "mitigations=" cmdline option for toggling
  * optional CPU mitigations.
  */
 enum cpu_mitigations {
         CPU_MITIGATIONS_OFF,
         CPU_MITIGATIONS_AUTO,
         CPU_MITIGATIONS_AUTO_NOSMT,
 };
 
 static enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO;
 
 static int __init mitigations_parse_cmdline(char *arg)
 {
         if (!strcmp(arg, "off"))
                 cpu_mitigations = CPU_MITIGATIONS_OFF;
         else if (!strcmp(arg, "auto"))
                 cpu_mitigations = CPU_MITIGATIONS_AUTO;
         else if (!strcmp(arg, "auto,nosmt"))
                 cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
         else
                 pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n",
                         arg);
 
         return 0;
 }
 
 /* mitigations=off */
 bool cpu_mitigations_off(void)
 {
         return cpu_mitigations == CPU_MITIGATIONS_OFF;
 }
 EXPORT_SYMBOL_GPL(cpu_mitigations_off);
 
 /* mitigations=auto,nosmt */
 bool cpu_mitigations_auto_nosmt(void)
 {
         return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
 }
 EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);
 #else
 static int __init mitigations_parse_cmdline(char *arg)
 {
         pr_crit("Kernel compiled without mitigations, ignoring 'mitigations'; system may still be vulnerable\n");
         return 0;
 }
 #endif
 early_param("mitigations", mitigations_parse_cmdline);
 

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