// SPDX-License-Identifier: GPL-2.0-only

  /* Kernel thread helper functions.
   *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
   *

   * 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/sched.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 <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. */

  	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;

  	void *data;

  	struct completion parked;

  	struct completion exited;

  #ifdef CONFIG_BLK_CGROUP

  	struct cgroup_subsys_state *blkcg_css;
  #endif

  };

  enum KTHREAD_BITS {
  	KTHREAD_IS_PER_CPU = 0,
  	KTHREAD_SHOULD_STOP,
  	KTHREAD_SHOULD_PARK,

  };

  static inline void set_kthread_struct(void *kthread)
  {
  	/*
  	 * We abuse ->set_child_tid to avoid the new member and because it
  	 * can't be wrongly copied by copy_process(). We also rely on fact
  	 * that the caller can't exec, so PF_KTHREAD can't be cleared.
  	 */
  	current->set_child_tid = (__force void __user *)kthread;
  }

  
  static inline struct kthread *to_kthread(struct task_struct *k)
  {

  	WARN_ON(!(k->flags & PF_KTHREAD));
  	return (__force void *)k->set_child_tid;

  }

  void free_kthread_struct(struct task_struct *k)
  {

  	struct kthread *kthread;

  	/*
  	 * Can be NULL if this kthread was created by kernel_thread()
  	 * or if kmalloc() in kthread() failed.
  	 */

  	kthread = to_kthread(k);

  #ifdef CONFIG_BLK_CGROUP

  	WARN_ON_ONCE(kthread && kthread->blkcg_css);
  #endif
  	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);

  bool __kthread_should_park(struct task_struct *k)
  {
  	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(k)->flags);
  }
  EXPORT_SYMBOL_GPL(__kthread_should_park);

  /**

   * 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);

  
  /**

   * 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_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;
  }

  /**

   * 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;
  
  	probe_kernel_read(&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);

  static int kthread(void *_create)
  {

  	/* 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 = kzalloc(sizeof(*self), GFP_KERNEL);

  	set_kthread_struct(self);

  	/* If user was SIGKILLed, I release the structure. */
  	done = xchg(&create->done, NULL);
  	if (!done) {
  		kfree(create);
  		do_exit(-EINTR);
  	}

  
  	if (!self) {
  		create->result = ERR_PTR(-ENOMEM);
  		complete(done);
  		do_exit(-ENOMEM);
  	}

  	self->data = data;
  	init_completion(&self->exited);
  	init_completion(&self->parked);
  	current->vfork_done = &self->exited;

  	/* 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);
  	}

  	do_exit(ret);

  }

  /* called from do_fork() 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, CLONE_FS | CLONE_FILES | SIGCHLD);

  	if (pid < 0) {

  		/* If user was SIGKILLed, I release the structure. */
  		struct completion *done = xchg(&create->done, NULL);
  
  		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;

  
  	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 SIGKILLed 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;
  	if (!IS_ERR(task)) {

  		static const struct sched_param param = { .sched_priority = 0 };

  		char name[TASK_COMM_LEN];

  		/*
  		 * task is already visible to other tasks, so updating
  		 * COMM must be protected.
  		 */
  		vsnprintf(name, sizeof(name), namefmt, args);
  		set_task_comm(task, name);

  		/*
  		 * root may have changed our (kthreadd's) priority or CPU mask.
  		 * The kernel thread should not inherit these properties.
  		 */

  		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
  		set_cpus_allowed_ptr(task, cpu_all_mask);

  	}

  	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 call do_exit() 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, long 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, long 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
   * The thread will be woken and put into park mode.
   */
  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. */

  	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
  	to_kthread(p)->cpu = cpu;

  	return p;
  }

  /**
   * 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);

  	/*

  	 * 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 do_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);

  	wake_up_process(k);
  	wait_for_completion(&kthread->exited);

  	ret = k->exit_code;

  	put_task_struct(k);

  	trace_sched_kthread_stop_ret(ret);

  	return ret;
  }

  EXPORT_SYMBOL(kthread_stop);

  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, cpu_all_mask);

  	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) {
  		__set_current_state(TASK_RUNNING);
  		work->func(work);

  	} else if (!freezing(current))
  		schedule();
  
  	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 worker was SIGKILLed.
   */
  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
   *	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).
   *
   * 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 worker was SIGKILLed.
   */
  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);

  
  	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);
  	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);

  /*
   * This function removes the work from the worker queue. Also it makes sure
   * that it won't get queued later via the delayed work's 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, bool is_dwork,
  				  unsigned long *flags)
  {
  	/* Try to cancel the timer if exists. */
  	if (is_dwork) {
  		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--;
  	}
  
  	/*
  	 * 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: %true if @dwork was pending and its timer was modified,
   * %false 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 %false here. 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 = false;

  	raw_spin_lock_irqsave(&worker->lock, flags);

  
  	/* Do not bother with canceling when never queued. */
  	if (!work->worker)
  		goto fast_queue;
  
  	/* Work must not be used with >1 worker, see kthread_queue_work() */
  	WARN_ON_ONCE(work->worker != worker);
  
  	/* Do not fight with another command that is canceling this work. */
  	if (work->canceling)
  		goto out;
  
  	ret = __kthread_cancel_work(work, true, &flags);
  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);
  
  	ret = __kthread_cancel_work(work, is_dwork, &flags);
  
  	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.
   */
  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->work_list));
  	kfree(worker);
  }
  EXPORT_SYMBOL(kthread_destroy_worker);

  #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;
  }
  EXPORT_SYMBOL(kthread_blkcg);
  #endif