TOMOYO Linux Cross Reference
Linux/kernel/kthread.c

   // SPDX-License-Identifier: GPL-2.0-only
   /* Kernel thread helper functions.
    *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
    *   Copyright (C) 2009 Red Hat, Inc.
    *
    * Creation is done via kthreadd, so that we get a clean environment
    * even if we're invoked from userspace (think modprobe, hotplug cpu,
    * etc.).
    */
  #include <uapi/linux/sched/types.h>
  #include <linux/mm.h>
  #include <linux/mmu_context.h>
  #include <linux/sched.h>
  #include <linux/sched/mm.h>
  #include <linux/sched/task.h>
  #include <linux/kthread.h>
  #include <linux/completion.h>
  #include <linux/err.h>
  #include <linux/cgroup.h>
  #include <linux/cpuset.h>
  #include <linux/unistd.h>
  #include <linux/file.h>
  #include <linux/export.h>
  #include <linux/mutex.h>
  #include <linux/slab.h>
  #include <linux/freezer.h>
  #include <linux/ptrace.h>
  #include <linux/uaccess.h>
  #include <linux/numa.h>
  #include <linux/sched/isolation.h>
  #include <trace/events/sched.h>
  
  
  static DEFINE_SPINLOCK(kthread_create_lock);
  static LIST_HEAD(kthread_create_list);
  struct task_struct *kthreadd_task;
  
  struct kthread_create_info
  {
          /* Information passed to kthread() from kthreadd. */
          char *full_name;
          int (*threadfn)(void *data);
          void *data;
          int node;
  
          /* Result passed back to kthread_create() from kthreadd. */
          struct task_struct *result;
          struct completion *done;
  
          struct list_head list;
  };
  
  struct kthread {
          unsigned long flags;
          unsigned int cpu;
          int result;
          int (*threadfn)(void *);
          void *data;
          struct completion parked;
          struct completion exited;
  #ifdef CONFIG_BLK_CGROUP
          struct cgroup_subsys_state *blkcg_css;
  #endif
          /* To store the full name if task comm is truncated. */
          char *full_name;
  };
  
  enum KTHREAD_BITS {
          KTHREAD_IS_PER_CPU = 0,
          KTHREAD_SHOULD_STOP,
          KTHREAD_SHOULD_PARK,
  };
  
  static inline struct kthread *to_kthread(struct task_struct *k)
  {
          WARN_ON(!(k->flags & PF_KTHREAD));
          return k->worker_private;
  }
  
  /*
   * Variant of to_kthread() that doesn't assume @p is a kthread.
   *
   * Per construction; when:
   *
   *   (p->flags & PF_KTHREAD) && p->worker_private
   *
   * the task is both a kthread and struct kthread is persistent. However
   * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
   * begin_new_exec()).
   */
  static inline struct kthread *__to_kthread(struct task_struct *p)
  {
          void *kthread = p->worker_private;
          if (kthread && !(p->flags & PF_KTHREAD))
                  kthread = NULL;
          return kthread;
  }
  
  void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk)
 {
         struct kthread *kthread = to_kthread(tsk);
 
         if (!kthread || !kthread->full_name) {
                 __get_task_comm(buf, buf_size, tsk);
                 return;
         }
 
         strscpy_pad(buf, kthread->full_name, buf_size);
 }
 
 bool set_kthread_struct(struct task_struct *p)
 {
         struct kthread *kthread;
 
         if (WARN_ON_ONCE(to_kthread(p)))
                 return false;
 
         kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
         if (!kthread)
                 return false;
 
         init_completion(&kthread->exited);
         init_completion(&kthread->parked);
         p->vfork_done = &kthread->exited;
 
         p->worker_private = kthread;
         return true;
 }
 
 void free_kthread_struct(struct task_struct *k)
 {
         struct kthread *kthread;
 
         /*
          * Can be NULL if kmalloc() in set_kthread_struct() failed.
          */
         kthread = to_kthread(k);
         if (!kthread)
                 return;
 
 #ifdef CONFIG_BLK_CGROUP
         WARN_ON_ONCE(kthread->blkcg_css);
 #endif
         k->worker_private = NULL;
         kfree(kthread->full_name);
         kfree(kthread);
 }
 
 /**
  * kthread_should_stop - should this kthread return now?
  *
  * When someone calls kthread_stop() on your kthread, it will be woken
  * and this will return true.  You should then return, and your return
  * value will be passed through to kthread_stop().
  */
 bool kthread_should_stop(void)
 {
         return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
 }
 EXPORT_SYMBOL(kthread_should_stop);
 
 static bool __kthread_should_park(struct task_struct *k)
 {
         return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(k)->flags);
 }
 
 /**
  * kthread_should_park - should this kthread park now?
  *
  * When someone calls kthread_park() on your kthread, it will be woken
  * and this will return true.  You should then do the necessary
  * cleanup and call kthread_parkme()
  *
  * Similar to kthread_should_stop(), but this keeps the thread alive
  * and in a park position. kthread_unpark() "restarts" the thread and
  * calls the thread function again.
  */
 bool kthread_should_park(void)
 {
         return __kthread_should_park(current);
 }
 EXPORT_SYMBOL_GPL(kthread_should_park);
 
 bool kthread_should_stop_or_park(void)
 {
         struct kthread *kthread = __to_kthread(current);
 
         if (!kthread)
                 return false;
 
         return kthread->flags & (BIT(KTHREAD_SHOULD_STOP) | BIT(KTHREAD_SHOULD_PARK));
 }
 
 /**
  * kthread_freezable_should_stop - should this freezable kthread return now?
  * @was_frozen: optional out parameter, indicates whether %current was frozen
  *
  * kthread_should_stop() for freezable kthreads, which will enter
  * refrigerator if necessary.  This function is safe from kthread_stop() /
  * freezer deadlock and freezable kthreads should use this function instead
  * of calling try_to_freeze() directly.
  */
 bool kthread_freezable_should_stop(bool *was_frozen)
 {
         bool frozen = false;
 
         might_sleep();
 
         if (unlikely(freezing(current)))
                 frozen = __refrigerator(true);
 
         if (was_frozen)
                 *was_frozen = frozen;
 
         return kthread_should_stop();
 }
 EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
 
 /**
  * kthread_func - return the function specified on kthread creation
  * @task: kthread task in question
  *
  * Returns NULL if the task is not a kthread.
  */
 void *kthread_func(struct task_struct *task)
 {
         struct kthread *kthread = __to_kthread(task);
         if (kthread)
                 return kthread->threadfn;
         return NULL;
 }
 EXPORT_SYMBOL_GPL(kthread_func);
 
 /**
  * kthread_data - return data value specified on kthread creation
  * @task: kthread task in question
  *
  * Return the data value specified when kthread @task was created.
  * The caller is responsible for ensuring the validity of @task when
  * calling this function.
  */
 void *kthread_data(struct task_struct *task)
 {
         return to_kthread(task)->data;
 }
 EXPORT_SYMBOL_GPL(kthread_data);
 
 /**
  * kthread_probe_data - speculative version of kthread_data()
  * @task: possible kthread task in question
  *
  * @task could be a kthread task.  Return the data value specified when it
  * was created if accessible.  If @task isn't a kthread task or its data is
  * inaccessible for any reason, %NULL is returned.  This function requires
  * that @task itself is safe to dereference.
  */
 void *kthread_probe_data(struct task_struct *task)
 {
         struct kthread *kthread = __to_kthread(task);
         void *data = NULL;
 
         if (kthread)
                 copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
         return data;
 }
 
 static void __kthread_parkme(struct kthread *self)
 {
         for (;;) {
                 /*
                  * TASK_PARKED is a special state; we must serialize against
                  * possible pending wakeups to avoid store-store collisions on
                  * task->state.
                  *
                  * Such a collision might possibly result in the task state
                  * changin from TASK_PARKED and us failing the
                  * wait_task_inactive() in kthread_park().
                  */
                 set_special_state(TASK_PARKED);
                 if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
                         break;
 
                 /*
                  * Thread is going to call schedule(), do not preempt it,
                  * or the caller of kthread_park() may spend more time in
                  * wait_task_inactive().
                  */
                 preempt_disable();
                 complete(&self->parked);
                 schedule_preempt_disabled();
                 preempt_enable();
         }
         __set_current_state(TASK_RUNNING);
 }
 
 void kthread_parkme(void)
 {
         __kthread_parkme(to_kthread(current));
 }
 EXPORT_SYMBOL_GPL(kthread_parkme);
 
 /**
  * kthread_exit - Cause the current kthread return @result to kthread_stop().
  * @result: The integer value to return to kthread_stop().
  *
  * While kthread_exit can be called directly, it exists so that
  * functions which do some additional work in non-modular code such as
  * module_put_and_kthread_exit can be implemented.
  *
  * Does not return.
  */
 void __noreturn kthread_exit(long result)
 {
         struct kthread *kthread = to_kthread(current);
         kthread->result = result;
         do_exit(0);
 }
 EXPORT_SYMBOL(kthread_exit);
 
 /**
  * kthread_complete_and_exit - Exit the current kthread.
  * @comp: Completion to complete
  * @code: The integer value to return to kthread_stop().
  *
  * If present, complete @comp and then return code to kthread_stop().
  *
  * A kernel thread whose module may be removed after the completion of
  * @comp can use this function to exit safely.
  *
  * Does not return.
  */
 void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
 {
         if (comp)
                 complete(comp);
 
         kthread_exit(code);
 }
 EXPORT_SYMBOL(kthread_complete_and_exit);
 
 static int kthread(void *_create)
 {
         static const struct sched_param param = { .sched_priority = 0 };
         /* Copy data: it's on kthread's stack */
         struct kthread_create_info *create = _create;
         int (*threadfn)(void *data) = create->threadfn;
         void *data = create->data;
         struct completion *done;
         struct kthread *self;
         int ret;
 
         self = to_kthread(current);
 
         /* Release the structure when caller killed by a fatal signal. */
         done = xchg(&create->done, NULL);
         if (!done) {
                 kfree(create->full_name);
                 kfree(create);
                 kthread_exit(-EINTR);
         }
 
         self->full_name = create->full_name;
         self->threadfn = threadfn;
         self->data = data;
 
         /*
          * The new thread inherited kthreadd's priority and CPU mask. Reset
          * back to default in case they have been changed.
          */
         sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
         set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_KTHREAD));
 
         /* OK, tell user we're spawned, wait for stop or wakeup */
         __set_current_state(TASK_UNINTERRUPTIBLE);
         create->result = current;
         /*
          * Thread is going to call schedule(), do not preempt it,
          * or the creator may spend more time in wait_task_inactive().
          */
         preempt_disable();
         complete(done);
         schedule_preempt_disabled();
         preempt_enable();
 
         ret = -EINTR;
         if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
                 cgroup_kthread_ready();
                 __kthread_parkme(self);
                 ret = threadfn(data);
         }
         kthread_exit(ret);
 }
 
 /* called from kernel_clone() to get node information for about to be created task */
 int tsk_fork_get_node(struct task_struct *tsk)
 {
 #ifdef CONFIG_NUMA
         if (tsk == kthreadd_task)
                 return tsk->pref_node_fork;
 #endif
         return NUMA_NO_NODE;
 }
 
 static void create_kthread(struct kthread_create_info *create)
 {
         int pid;
 
 #ifdef CONFIG_NUMA
         current->pref_node_fork = create->node;
 #endif
         /* We want our own signal handler (we take no signals by default). */
         pid = kernel_thread(kthread, create, create->full_name,
                             CLONE_FS | CLONE_FILES | SIGCHLD);
         if (pid < 0) {
                 /* Release the structure when caller killed by a fatal signal. */
                 struct completion *done = xchg(&create->done, NULL);
 
                 kfree(create->full_name);
                 if (!done) {
                         kfree(create);
                         return;
                 }
                 create->result = ERR_PTR(pid);
                 complete(done);
         }
 }
 
 static __printf(4, 0)
 struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
                                                     void *data, int node,
                                                     const char namefmt[],
                                                     va_list args)
 {
         DECLARE_COMPLETION_ONSTACK(done);
         struct task_struct *task;
         struct kthread_create_info *create = kmalloc(sizeof(*create),
                                                      GFP_KERNEL);
 
         if (!create)
                 return ERR_PTR(-ENOMEM);
         create->threadfn = threadfn;
         create->data = data;
         create->node = node;
         create->done = &done;
         create->full_name = kvasprintf(GFP_KERNEL, namefmt, args);
         if (!create->full_name) {
                 task = ERR_PTR(-ENOMEM);
                 goto free_create;
         }
 
         spin_lock(&kthread_create_lock);
         list_add_tail(&create->list, &kthread_create_list);
         spin_unlock(&kthread_create_lock);
 
         wake_up_process(kthreadd_task);
         /*
          * Wait for completion in killable state, for I might be chosen by
          * the OOM killer while kthreadd is trying to allocate memory for
          * new kernel thread.
          */
         if (unlikely(wait_for_completion_killable(&done))) {
                 /*
                  * If I was killed by a fatal signal before kthreadd (or new
                  * kernel thread) calls complete(), leave the cleanup of this
                  * structure to that thread.
                  */
                 if (xchg(&create->done, NULL))
                         return ERR_PTR(-EINTR);
                 /*
                  * kthreadd (or new kernel thread) will call complete()
                  * shortly.
                  */
                 wait_for_completion(&done);
         }
         task = create->result;
 free_create:
         kfree(create);
         return task;
 }
 
 /**
  * kthread_create_on_node - create a kthread.
  * @threadfn: the function to run until signal_pending(current).
  * @data: data ptr for @threadfn.
  * @node: task and thread structures for the thread are allocated on this node
  * @namefmt: printf-style name for the thread.
  *
  * Description: This helper function creates and names a kernel
  * thread.  The thread will be stopped: use wake_up_process() to start
  * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
  * is affine to all CPUs.
  *
  * If thread is going to be bound on a particular cpu, give its node
  * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
  * When woken, the thread will run @threadfn() with @data as its
  * argument. @threadfn() can either return directly if it is a
  * standalone thread for which no one will call kthread_stop(), or
  * return when 'kthread_should_stop()' is true (which means
  * kthread_stop() has been called).  The return value should be zero
  * or a negative error number; it will be passed to kthread_stop().
  *
  * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
  */
 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
                                            void *data, int node,
                                            const char namefmt[],
                                            ...)
 {
         struct task_struct *task;
         va_list args;
 
         va_start(args, namefmt);
         task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
         va_end(args);
 
         return task;
 }
 EXPORT_SYMBOL(kthread_create_on_node);
 
 static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, unsigned int state)
 {
         unsigned long flags;
 
         if (!wait_task_inactive(p, state)) {
                 WARN_ON(1);
                 return;
         }
 
         /* It's safe because the task is inactive. */
         raw_spin_lock_irqsave(&p->pi_lock, flags);
         do_set_cpus_allowed(p, mask);
         p->flags |= PF_NO_SETAFFINITY;
         raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 }
 
 static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int state)
 {
         __kthread_bind_mask(p, cpumask_of(cpu), state);
 }
 
 void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
 {
         __kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
 }
 
 /**
  * kthread_bind - bind a just-created kthread to a cpu.
  * @p: thread created by kthread_create().
  * @cpu: cpu (might not be online, must be possible) for @k to run on.
  *
  * Description: This function is equivalent to set_cpus_allowed(),
  * except that @cpu doesn't need to be online, and the thread must be
  * stopped (i.e., just returned from kthread_create()).
  */
 void kthread_bind(struct task_struct *p, unsigned int cpu)
 {
         __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(kthread_bind);
 
 /**
  * kthread_create_on_cpu - Create a cpu bound kthread
  * @threadfn: the function to run until signal_pending(current).
  * @data: data ptr for @threadfn.
  * @cpu: The cpu on which the thread should be bound,
  * @namefmt: printf-style name for the thread. Format is restricted
  *           to "name.*%u". Code fills in cpu number.
  *
  * Description: This helper function creates and names a kernel thread
  */
 struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
                                           void *data, unsigned int cpu,
                                           const char *namefmt)
 {
         struct task_struct *p;
 
         p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
                                    cpu);
         if (IS_ERR(p))
                 return p;
         kthread_bind(p, cpu);
         /* CPU hotplug need to bind once again when unparking the thread. */
         to_kthread(p)->cpu = cpu;
         return p;
 }
 EXPORT_SYMBOL(kthread_create_on_cpu);
 
 void kthread_set_per_cpu(struct task_struct *k, int cpu)
 {
         struct kthread *kthread = to_kthread(k);
         if (!kthread)
                 return;
 
         WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
 
         if (cpu < 0) {
                 clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
                 return;
         }
 
         kthread->cpu = cpu;
         set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 }
 
 bool kthread_is_per_cpu(struct task_struct *p)
 {
         struct kthread *kthread = __to_kthread(p);
         if (!kthread)
                 return false;
 
         return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 }
 
 /**
  * kthread_unpark - unpark a thread created by kthread_create().
  * @k:          thread created by kthread_create().
  *
  * Sets kthread_should_park() for @k to return false, wakes it, and
  * waits for it to return. If the thread is marked percpu then its
  * bound to the cpu again.
  */
 void kthread_unpark(struct task_struct *k)
 {
         struct kthread *kthread = to_kthread(k);
 
         if (!test_bit(KTHREAD_SHOULD_PARK, &kthread->flags))
                 return;
         /*
          * Newly created kthread was parked when the CPU was offline.
          * The binding was lost and we need to set it again.
          */
         if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
                 __kthread_bind(k, kthread->cpu, TASK_PARKED);
 
         clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
         /*
          * __kthread_parkme() will either see !SHOULD_PARK or get the wakeup.
          */
         wake_up_state(k, TASK_PARKED);
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
 
 /**
  * kthread_park - park a thread created by kthread_create().
  * @k: thread created by kthread_create().
  *
  * Sets kthread_should_park() for @k to return true, wakes it, and
  * waits for it to return. This can also be called after kthread_create()
  * instead of calling wake_up_process(): the thread will park without
  * calling threadfn().
  *
  * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
  * If called by the kthread itself just the park bit is set.
  */
 int kthread_park(struct task_struct *k)
 {
         struct kthread *kthread = to_kthread(k);
 
         if (WARN_ON(k->flags & PF_EXITING))
                 return -ENOSYS;
 
         if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
                 return -EBUSY;
 
         set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
         if (k != current) {
                 wake_up_process(k);
                 /*
                  * Wait for __kthread_parkme() to complete(), this means we
                  * _will_ have TASK_PARKED and are about to call schedule().
                  */
                 wait_for_completion(&kthread->parked);
                 /*
                  * Now wait for that schedule() to complete and the task to
                  * get scheduled out.
                  */
                 WARN_ON_ONCE(!wait_task_inactive(k, TASK_PARKED));
         }
 
         return 0;
 }
 EXPORT_SYMBOL_GPL(kthread_park);
 
 /**
  * kthread_stop - stop a thread created by kthread_create().
  * @k: thread created by kthread_create().
  *
  * Sets kthread_should_stop() for @k to return true, wakes it, and
  * waits for it to exit. This can also be called after kthread_create()
  * instead of calling wake_up_process(): the thread will exit without
  * calling threadfn().
  *
  * If threadfn() may call kthread_exit() itself, the caller must ensure
  * task_struct can't go away.
  *
  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
  * was never called.
  */
 int kthread_stop(struct task_struct *k)
 {
         struct kthread *kthread;
         int ret;
 
         trace_sched_kthread_stop(k);
 
         get_task_struct(k);
         kthread = to_kthread(k);
         set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
         kthread_unpark(k);
         set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
         wake_up_process(k);
         wait_for_completion(&kthread->exited);
         ret = kthread->result;
         put_task_struct(k);
 
         trace_sched_kthread_stop_ret(ret);
         return ret;
 }
 EXPORT_SYMBOL(kthread_stop);
 
 /**
  * kthread_stop_put - stop a thread and put its task struct
  * @k: thread created by kthread_create().
  *
  * Stops a thread created by kthread_create() and put its task_struct.
  * Only use when holding an extra task struct reference obtained by
  * calling get_task_struct().
  */
 int kthread_stop_put(struct task_struct *k)
 {
         int ret;
 
         ret = kthread_stop(k);
         put_task_struct(k);
         return ret;
 }
 EXPORT_SYMBOL(kthread_stop_put);
 
 int kthreadd(void *unused)
 {
         struct task_struct *tsk = current;
 
         /* Setup a clean context for our children to inherit. */
         set_task_comm(tsk, "kthreadd");
         ignore_signals(tsk);
         set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD));
         set_mems_allowed(node_states[N_MEMORY]);
 
         current->flags |= PF_NOFREEZE;
         cgroup_init_kthreadd();
 
         for (;;) {
                 set_current_state(TASK_INTERRUPTIBLE);
                 if (list_empty(&kthread_create_list))
                         schedule();
                 __set_current_state(TASK_RUNNING);
 
                 spin_lock(&kthread_create_lock);
                 while (!list_empty(&kthread_create_list)) {
                         struct kthread_create_info *create;
 
                         create = list_entry(kthread_create_list.next,
                                             struct kthread_create_info, list);
                         list_del_init(&create->list);
                         spin_unlock(&kthread_create_lock);
 
                         create_kthread(create);
 
                         spin_lock(&kthread_create_lock);
                 }
                 spin_unlock(&kthread_create_lock);
         }
 
         return 0;
 }
 
 void __kthread_init_worker(struct kthread_worker *worker,
                                 const char *name,
                                 struct lock_class_key *key)
 {
         memset(worker, 0, sizeof(struct kthread_worker));
         raw_spin_lock_init(&worker->lock);
         lockdep_set_class_and_name(&worker->lock, key, name);
         INIT_LIST_HEAD(&worker->work_list);
         INIT_LIST_HEAD(&worker->delayed_work_list);
 }
 EXPORT_SYMBOL_GPL(__kthread_init_worker);
 
 /**
  * kthread_worker_fn - kthread function to process kthread_worker
  * @worker_ptr: pointer to initialized kthread_worker
  *
  * This function implements the main cycle of kthread worker. It processes
  * work_list until it is stopped with kthread_stop(). It sleeps when the queue
  * is empty.
  *
  * The works are not allowed to keep any locks, disable preemption or interrupts
  * when they finish. There is defined a safe point for freezing when one work
  * finishes and before a new one is started.
  *
  * Also the works must not be handled by more than one worker at the same time,
  * see also kthread_queue_work().
  */
 int kthread_worker_fn(void *worker_ptr)
 {
         struct kthread_worker *worker = worker_ptr;
         struct kthread_work *work;
 
         /*
          * FIXME: Update the check and remove the assignment when all kthread
          * worker users are created using kthread_create_worker*() functions.
          */
         WARN_ON(worker->task && worker->task != current);
         worker->task = current;
 
         if (worker->flags & KTW_FREEZABLE)
                 set_freezable();
 
 repeat:
         set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 
         if (kthread_should_stop()) {
                 __set_current_state(TASK_RUNNING);
                 raw_spin_lock_irq(&worker->lock);
                 worker->task = NULL;
                 raw_spin_unlock_irq(&worker->lock);
                 return 0;
         }
 
         work = NULL;
         raw_spin_lock_irq(&worker->lock);
         if (!list_empty(&worker->work_list)) {
                 work = list_first_entry(&worker->work_list,
                                         struct kthread_work, node);
                 list_del_init(&work->node);
         }
         worker->current_work = work;
         raw_spin_unlock_irq(&worker->lock);
 
         if (work) {
                 kthread_work_func_t func = work->func;
                 __set_current_state(TASK_RUNNING);
                 trace_sched_kthread_work_execute_start(work);
                 work->func(work);
                 /*
                  * Avoid dereferencing work after this point.  The trace
                  * event only cares about the address.
                  */
                 trace_sched_kthread_work_execute_end(work, func);
         } else if (!freezing(current)) {
                 schedule();
         } else {
                 /*
                  * Handle the case where the current remains
                  * TASK_INTERRUPTIBLE. try_to_freeze() expects
                  * the current to be TASK_RUNNING.
                  */
                 __set_current_state(TASK_RUNNING);
         }
 
         try_to_freeze();
         cond_resched();
         goto repeat;
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
 static __printf(3, 0) struct kthread_worker *
 __kthread_create_worker(int cpu, unsigned int flags,
                         const char namefmt[], va_list args)
 {
         struct kthread_worker *worker;
         struct task_struct *task;
         int node = NUMA_NO_NODE;
 
         worker = kzalloc(sizeof(*worker), GFP_KERNEL);
         if (!worker)
                 return ERR_PTR(-ENOMEM);
 
         kthread_init_worker(worker);
 
         if (cpu >= 0)
                 node = cpu_to_node(cpu);
 
         task = __kthread_create_on_node(kthread_worker_fn, worker,
                                                 node, namefmt, args);
         if (IS_ERR(task))
                 goto fail_task;
 
         if (cpu >= 0)
                 kthread_bind(task, cpu);
 
         worker->flags = flags;
         worker->task = task;
         wake_up_process(task);
         return worker;
 
 fail_task:
         kfree(worker);
         return ERR_CAST(task);
 }
 
 /**
  * kthread_create_worker - create a kthread worker
  * @flags: flags modifying the default behavior of the worker
  * @namefmt: printf-style name for the kthread worker (task).
  *
  * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
  * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
  * when the caller was killed by a fatal signal.
  */
 struct kthread_worker *
 kthread_create_worker(unsigned int flags, const char namefmt[], ...)
 {
         struct kthread_worker *worker;
         va_list args;
 
         va_start(args, namefmt);
         worker = __kthread_create_worker(-1, flags, namefmt, args);
         va_end(args);
 
         return worker;
 }
 EXPORT_SYMBOL(kthread_create_worker);
 
 /**
  * kthread_create_worker_on_cpu - create a kthread worker and bind it
  *      to a given CPU and the associated NUMA node.
  * @cpu: CPU number
  * @flags: flags modifying the default behavior of the worker
  * @namefmt: printf-style name for the kthread worker (task).
  *
  * Use a valid CPU number if you want to bind the kthread worker
  * to the given CPU and the associated NUMA node.
  *
  * A good practice is to add the cpu number also into the worker name.
  * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
  *
  * CPU hotplug:
  * The kthread worker API is simple and generic. It just provides a way
  * to create, use, and destroy workers.
  *
  * It is up to the API user how to handle CPU hotplug. They have to decide
  * how to handle pending work items, prevent queuing new ones, and
  * restore the functionality when the CPU goes off and on. There are a
  * few catches:
  *
  *    - CPU affinity gets lost when it is scheduled on an offline CPU.
  *
  *    - The worker might not exist when the CPU was off when the user
  *      created the workers.
  *
  * Good practice is to implement two CPU hotplug callbacks and to
  * destroy/create the worker when the CPU goes down/up.
  *
  * Return:
  * The pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
  * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
  * when the caller was killed by a fatal signal.
  */
 struct kthread_worker *
 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
                              const char namefmt[], ...)
 {
         struct kthread_worker *worker;
         va_list args;
 
         va_start(args, namefmt);
         worker = __kthread_create_worker(cpu, flags, namefmt, args);
         va_end(args);
 
         return worker;
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
 /*
  * Returns true when the work could not be queued at the moment.
  * It happens when it is already pending in a worker list
  * or when it is being cancelled.
  */
 static inline bool queuing_blocked(struct kthread_worker *worker,
                                    struct kthread_work *work)
 {
         lockdep_assert_held(&worker->lock);
 
         return !list_empty(&work->node) || work->canceling;
 }
 
 static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
                                              struct kthread_work *work)
 {
         lockdep_assert_held(&worker->lock);
         WARN_ON_ONCE(!list_empty(&work->node));
         /* Do not use a work with >1 worker, see kthread_queue_work() */
         WARN_ON_ONCE(work->worker && work->worker != worker);
 }
 
 /* insert @work before @pos in @worker */
 static void kthread_insert_work(struct kthread_worker *worker,
                                 struct kthread_work *work,
                                 struct list_head *pos)
 {
         kthread_insert_work_sanity_check(worker, work);
 
         trace_sched_kthread_work_queue_work(worker, work);
 
         list_add_tail(&work->node, pos);
         work->worker = worker;
         if (!worker->current_work && likely(worker->task))
                 wake_up_process(worker->task);
 }
 
 /**
  * kthread_queue_work - queue a kthread_work
  * @worker: target kthread_worker
  * @work: kthread_work to queue
  *
  * Queue @work to work processor @task for async execution.  @task
  * must have been created with kthread_worker_create().  Returns %true
  * if @work was successfully queued, %false if it was already pending.
  *
  * Reinitialize the work if it needs to be used by another worker.
  * For example, when the worker was stopped and started again.
  */
 bool kthread_queue_work(struct kthread_worker *worker,
                         struct kthread_work *work)
 {
         bool ret = false;
         unsigned long flags;
 
         raw_spin_lock_irqsave(&worker->lock, flags);
         if (!queuing_blocked(worker, work)) {
                 kthread_insert_work(worker, work, &worker->work_list);
                 ret = true;
         }
         raw_spin_unlock_irqrestore(&worker->lock, flags);
         return ret;
 }
 EXPORT_SYMBOL_GPL(kthread_queue_work);
 
 /**
  * kthread_delayed_work_timer_fn - callback that queues the associated kthread
  *      delayed work when the timer expires.
  * @t: pointer to the expired timer
  *
  * The format of the function is defined by struct timer_list.
  * It should have been called from irqsafe timer with irq already off.
  */
 void kthread_delayed_work_timer_fn(struct timer_list *t)
 {
         struct kthread_delayed_work *dwork = from_timer(dwork, t, timer);
         struct kthread_work *work = &dwork->work;
         struct kthread_worker *worker = work->worker;
         unsigned long flags;
 
         /*
          * This might happen when a pending work is reinitialized.
          * It means that it is used a wrong way.
          */
         if (WARN_ON_ONCE(!worker))
                 return;
 
         raw_spin_lock_irqsave(&worker->lock, flags);
         /* Work must not be used with >1 worker, see kthread_queue_work(). */
         WARN_ON_ONCE(work->worker != worker);
 
         /* Move the work from worker->delayed_work_list. */
         WARN_ON_ONCE(list_empty(&work->node));
         list_del_init(&work->node);
         if (!work->canceling)
                 kthread_insert_work(worker, work, &worker->work_list);
 
         raw_spin_unlock_irqrestore(&worker->lock, flags);
 }
 EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
 
 static void __kthread_queue_delayed_work(struct kthread_worker *worker,
                                          struct kthread_delayed_work *dwork,
                                          unsigned long delay)
 {
         struct timer_list *timer = &dwork->timer;
         struct kthread_work *work = &dwork->work;
 
         WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);
 
         /*
          * If @delay is 0, queue @dwork->work immediately.  This is for
          * both optimization and correctness.  The earliest @timer can
          * expire is on the closest next tick and delayed_work users depend
          * on that there's no such delay when @delay is 0.
          */
         if (!delay) {
                 kthread_insert_work(worker, work, &worker->work_list);
                 return;
         }
 
         /* Be paranoid and try to detect possible races already now. */
         kthread_insert_work_sanity_check(worker, work);
 
         list_add(&work->node, &worker->delayed_work_list);
         work->worker = worker;
         timer->expires = jiffies + delay;
         add_timer(timer);
 }
 
 /**
  * kthread_queue_delayed_work - queue the associated kthread work
  *      after a delay.
  * @worker: target kthread_worker
  * @dwork: kthread_delayed_work to queue
  * @delay: number of jiffies to wait before queuing
  *
  * If the work has not been pending it starts a timer that will queue
  * the work after the given @delay. If @delay is zero, it queues the
  * work immediately.
  *
  * Return: %false if the @work has already been pending. It means that
  * either the timer was running or the work was queued. It returns %true
  * otherwise.
  */
 bool kthread_queue_delayed_work(struct kthread_worker *worker,
                                 struct kthread_delayed_work *dwork,
                                 unsigned long delay)
 {
         struct kthread_work *work = &dwork->work;
         unsigned long flags;
         bool ret = false;
 
         raw_spin_lock_irqsave(&worker->lock, flags);
 
         if (!queuing_blocked(worker, work)) {
                 __kthread_queue_delayed_work(worker, dwork, delay);
                 ret = true;
         }
 
         raw_spin_unlock_irqrestore(&worker->lock, flags);
         return ret;
 }
 EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
 
 struct kthread_flush_work {
         struct kthread_work     work;
         struct completion       done;
 };
 
 static void kthread_flush_work_fn(struct kthread_work *work)
 {
         struct kthread_flush_work *fwork =
                 container_of(work, struct kthread_flush_work, work);
         complete(&fwork->done);
 }
 
 /**
  * kthread_flush_work - flush a kthread_work
  * @work: work to flush
  *
  * If @work is queued or executing, wait for it to finish execution.
  */
 void kthread_flush_work(struct kthread_work *work)
 {
         struct kthread_flush_work fwork = {
                 KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
                 COMPLETION_INITIALIZER_ONSTACK(fwork.done),
         };
         struct kthread_worker *worker;
         bool noop = false;
 
         worker = work->worker;
         if (!worker)
                 return;
 
         raw_spin_lock_irq(&worker->lock);
         /* Work must not be used with >1 worker, see kthread_queue_work(). */
         WARN_ON_ONCE(work->worker != worker);
 
         if (!list_empty(&work->node))
                 kthread_insert_work(worker, &fwork.work, work->node.next);
         else if (worker->current_work == work)
                 kthread_insert_work(worker, &fwork.work,
                                     worker->work_list.next);
         else
                 noop = true;
 
         raw_spin_unlock_irq(&worker->lock);
 
         if (!noop)
                 wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(kthread_flush_work);
 
 /*
  * Make sure that the timer is neither set nor running and could
  * not manipulate the work list_head any longer.
  *
  * The function is called under worker->lock. The lock is temporary
  * released but the timer can't be set again in the meantime.
  */
 static void kthread_cancel_delayed_work_timer(struct kthread_work *work,
                                               unsigned long *flags)
 {
         struct kthread_delayed_work *dwork =
                 container_of(work, struct kthread_delayed_work, work);
         struct kthread_worker *worker = work->worker;
 
         /*
          * del_timer_sync() must be called to make sure that the timer
          * callback is not running. The lock must be temporary released
          * to avoid a deadlock with the callback. In the meantime,
          * any queuing is blocked by setting the canceling counter.
          */
         work->canceling++;
         raw_spin_unlock_irqrestore(&worker->lock, *flags);
         del_timer_sync(&dwork->timer);
         raw_spin_lock_irqsave(&worker->lock, *flags);
         work->canceling--;
 }
 
 /*
  * This function removes the work from the worker queue.
  *
  * It is called under worker->lock. The caller must make sure that
  * the timer used by delayed work is not running, e.g. by calling
  * kthread_cancel_delayed_work_timer().
  *
  * The work might still be in use when this function finishes. See the
  * current_work proceed by the worker.
  *
  * Return: %true if @work was pending and successfully canceled,
  *      %false if @work was not pending
  */
 static bool __kthread_cancel_work(struct kthread_work *work)
 {
         /*
          * Try to remove the work from a worker list. It might either
          * be from worker->work_list or from worker->delayed_work_list.
          */
         if (!list_empty(&work->node)) {
                 list_del_init(&work->node);
                 return true;
         }
 
         return false;
 }
 
 /**
  * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
  * @worker: kthread worker to use
  * @dwork: kthread delayed work to queue
  * @delay: number of jiffies to wait before queuing
  *
  * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
  * modify @dwork's timer so that it expires after @delay. If @delay is zero,
  * @work is guaranteed to be queued immediately.
  *
  * Return: %false if @dwork was idle and queued, %true otherwise.
  *
  * A special case is when the work is being canceled in parallel.
  * It might be caused either by the real kthread_cancel_delayed_work_sync()
  * or yet another kthread_mod_delayed_work() call. We let the other command
  * win and return %true here. The return value can be used for reference
  * counting and the number of queued works stays the same. Anyway, the caller
  * is supposed to synchronize these operations a reasonable way.
  *
  * This function is safe to call from any context including IRQ handler.
  * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
  * for details.
  */
 bool kthread_mod_delayed_work(struct kthread_worker *worker,
                               struct kthread_delayed_work *dwork,
                               unsigned long delay)
 {
         struct kthread_work *work = &dwork->work;
         unsigned long flags;
         int ret;
 
         raw_spin_lock_irqsave(&worker->lock, flags);
 
         /* Do not bother with canceling when never queued. */
         if (!work->worker) {
                 ret = false;
                 goto fast_queue;
         }
 
         /* Work must not be used with >1 worker, see kthread_queue_work() */
         WARN_ON_ONCE(work->worker != worker);
 
         /*
          * Temporary cancel the work but do not fight with another command
          * that is canceling the work as well.
          *
          * It is a bit tricky because of possible races with another
          * mod_delayed_work() and cancel_delayed_work() callers.
          *
          * The timer must be canceled first because worker->lock is released
          * when doing so. But the work can be removed from the queue (list)
          * only when it can be queued again so that the return value can
          * be used for reference counting.
          */
         kthread_cancel_delayed_work_timer(work, &flags);
         if (work->canceling) {
                 /* The number of works in the queue does not change. */
                 ret = true;
                 goto out;
         }
         ret = __kthread_cancel_work(work);
 
 fast_queue:
         __kthread_queue_delayed_work(worker, dwork, delay);
 out:
         raw_spin_unlock_irqrestore(&worker->lock, flags);
         return ret;
 }
 EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
 
 static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
 {
         struct kthread_worker *worker = work->worker;
         unsigned long flags;
         int ret = false;
 
         if (!worker)
                 goto out;
 
         raw_spin_lock_irqsave(&worker->lock, flags);
         /* Work must not be used with >1 worker, see kthread_queue_work(). */
         WARN_ON_ONCE(work->worker != worker);
 
         if (is_dwork)
                 kthread_cancel_delayed_work_timer(work, &flags);
 
         ret = __kthread_cancel_work(work);
 
         if (worker->current_work != work)
                 goto out_fast;
 
         /*
          * The work is in progress and we need to wait with the lock released.
          * In the meantime, block any queuing by setting the canceling counter.
          */
         work->canceling++;
         raw_spin_unlock_irqrestore(&worker->lock, flags);
         kthread_flush_work(work);
         raw_spin_lock_irqsave(&worker->lock, flags);
         work->canceling--;
 
 out_fast:
         raw_spin_unlock_irqrestore(&worker->lock, flags);
 out:
         return ret;
 }
 
 /**
  * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
  * @work: the kthread work to cancel
  *
  * Cancel @work and wait for its execution to finish.  This function
  * can be used even if the work re-queues itself. On return from this
  * function, @work is guaranteed to be not pending or executing on any CPU.
  *
  * kthread_cancel_work_sync(&delayed_work->work) must not be used for
  * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
  *
  * The caller must ensure that the worker on which @work was last
  * queued can't be destroyed before this function returns.
  *
  * Return: %true if @work was pending, %false otherwise.
  */
 bool kthread_cancel_work_sync(struct kthread_work *work)
 {
         return __kthread_cancel_work_sync(work, false);
 }
 EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
 
 /**
  * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
  *      wait for it to finish.
  * @dwork: the kthread delayed work to cancel
  *
  * This is kthread_cancel_work_sync() for delayed works.
  *
  * Return: %true if @dwork was pending, %false otherwise.
  */
 bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
 {
         return __kthread_cancel_work_sync(&dwork->work, true);
 }
 EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
 
 /**
  * kthread_flush_worker - flush all current works on a kthread_worker
  * @worker: worker to flush
  *
  * Wait until all currently executing or pending works on @worker are
  * finished.
  */
 void kthread_flush_worker(struct kthread_worker *worker)
 {
         struct kthread_flush_work fwork = {
                 KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
                 COMPLETION_INITIALIZER_ONSTACK(fwork.done),
         };
 
         kthread_queue_work(worker, &fwork.work);
         wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(kthread_flush_worker);
 
 /**
  * kthread_destroy_worker - destroy a kthread worker
  * @worker: worker to be destroyed
  *
  * Flush and destroy @worker.  The simple flush is enough because the kthread
  * worker API is used only in trivial scenarios.  There are no multi-step state
  * machines needed.
  *
  * Note that this function is not responsible for handling delayed work, so
  * caller should be responsible for queuing or canceling all delayed work items
  * before invoke this function.
  */
 void kthread_destroy_worker(struct kthread_worker *worker)
 {
         struct task_struct *task;
 
         task = worker->task;
         if (WARN_ON(!task))
                 return;
 
         kthread_flush_worker(worker);
         kthread_stop(task);
         WARN_ON(!list_empty(&worker->delayed_work_list));
         WARN_ON(!list_empty(&worker->work_list));
         kfree(worker);
 }
 EXPORT_SYMBOL(kthread_destroy_worker);
 
 /**
  * kthread_use_mm - make the calling kthread operate on an address space
  * @mm: address space to operate on
  */
 void kthread_use_mm(struct mm_struct *mm)
 {
         struct mm_struct *active_mm;
         struct task_struct *tsk = current;
 
         WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
         WARN_ON_ONCE(tsk->mm);
 
         /*
          * It is possible for mm to be the same as tsk->active_mm, but
          * we must still mmgrab(mm) and mmdrop_lazy_tlb(active_mm),
          * because these references are not equivalent.
          */
         mmgrab(mm);
 
         task_lock(tsk);
         /* Hold off tlb flush IPIs while switching mm's */
         local_irq_disable();
         active_mm = tsk->active_mm;
         tsk->active_mm = mm;
         tsk->mm = mm;
         membarrier_update_current_mm(mm);
         switch_mm_irqs_off(active_mm, mm, tsk);
         local_irq_enable();
         task_unlock(tsk);
 #ifdef finish_arch_post_lock_switch
         finish_arch_post_lock_switch();
 #endif
 
         /*
          * When a kthread starts operating on an address space, the loop
          * in membarrier_{private,global}_expedited() may not observe
          * that tsk->mm, and not issue an IPI. Membarrier requires a
          * memory barrier after storing to tsk->mm, before accessing
          * user-space memory. A full memory barrier for membarrier
          * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by
          * mmdrop_lazy_tlb().
          */
         mmdrop_lazy_tlb(active_mm);
 }
 EXPORT_SYMBOL_GPL(kthread_use_mm);
 
 /**
  * kthread_unuse_mm - reverse the effect of kthread_use_mm()
  * @mm: address space to operate on
  */
 void kthread_unuse_mm(struct mm_struct *mm)
 {
         struct task_struct *tsk = current;
 
         WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
         WARN_ON_ONCE(!tsk->mm);
 
         task_lock(tsk);
         /*
          * When a kthread stops operating on an address space, the loop
          * in membarrier_{private,global}_expedited() may not observe
          * that tsk->mm, and not issue an IPI. Membarrier requires a
          * memory barrier after accessing user-space memory, before
          * clearing tsk->mm.
          */
         smp_mb__after_spinlock();
         local_irq_disable();
         tsk->mm = NULL;
         membarrier_update_current_mm(NULL);
         mmgrab_lazy_tlb(mm);
         /* active_mm is still 'mm' */
         enter_lazy_tlb(mm, tsk);
         local_irq_enable();
         task_unlock(tsk);
 
         mmdrop(mm);
 }
 EXPORT_SYMBOL_GPL(kthread_unuse_mm);
 
 #ifdef CONFIG_BLK_CGROUP
 /**
  * kthread_associate_blkcg - associate blkcg to current kthread
  * @css: the cgroup info
  *
  * Current thread must be a kthread. The thread is running jobs on behalf of
  * other threads. In some cases, we expect the jobs attach cgroup info of
  * original threads instead of that of current thread. This function stores
  * original thread's cgroup info in current kthread context for later
  * retrieval.
  */
 void kthread_associate_blkcg(struct cgroup_subsys_state *css)
 {
         struct kthread *kthread;
 
         if (!(current->flags & PF_KTHREAD))
                 return;
         kthread = to_kthread(current);
         if (!kthread)
                 return;
 
         if (kthread->blkcg_css) {
                 css_put(kthread->blkcg_css);
                 kthread->blkcg_css = NULL;
         }
         if (css) {
                 css_get(css);
                 kthread->blkcg_css = css;
         }
 }
 EXPORT_SYMBOL(kthread_associate_blkcg);
 
 /**
  * kthread_blkcg - get associated blkcg css of current kthread
  *
  * Current thread must be a kthread.
  */
 struct cgroup_subsys_state *kthread_blkcg(void)
 {
         struct kthread *kthread;
 
         if (current->flags & PF_KTHREAD) {
                 kthread = to_kthread(current);
                 if (kthread)
                         return kthread->blkcg_css;
         }
         return NULL;
 }
 #endif
 

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