/* 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 <linux/sched.h>
  #include <linux/kthread.h>
  #include <linux/completion.h>
  #include <linux/err.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 <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;

  };

  enum KTHREAD_BITS {
  	KTHREAD_IS_PER_CPU = 0,
  	KTHREAD_SHOULD_STOP,
  	KTHREAD_SHOULD_PARK,
  	KTHREAD_IS_PARKED,
  };

  #define __to_kthread(vfork)	\
  	container_of(vfork, struct kthread, exited)
  
  static inline struct kthread *to_kthread(struct task_struct *k)
  {
  	return __to_kthread(k->vfork_done);
  }
  
  static struct kthread *to_live_kthread(struct task_struct *k)
  {
  	struct completion *vfork = ACCESS_ONCE(k->vfork_done);
  	if (likely(vfork))
  		return __to_kthread(vfork);
  	return NULL;
  }

  /**
   * 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);

  /**

   * 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 test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
  }
  
  /**

   * 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;
  }

  /**
   * probe_kthread_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 *probe_kthread_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)
  {

  	__set_current_state(TASK_PARKED);

  	while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
  		if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
  			complete(&self->parked);
  		schedule();

  		__set_current_state(TASK_PARKED);

  	}
  	clear_bit(KTHREAD_IS_PARKED, &self->flags);
  	__set_current_state(TASK_RUNNING);
  }
  
  void kthread_parkme(void)
  {
  	__kthread_parkme(to_kthread(current));
  }

  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.flags = 0;

  	self.data = data;

  	init_completion(&self.exited);

  	init_completion(&self.parked);

  	current->vfork_done = &self.exited;

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

  	/* OK, tell user we're spawned, wait for stop or wakeup */

  	__set_current_state(TASK_UNINTERRUPTIBLE);

  	create->result = current;

  	complete(done);

  	schedule();

  	ret = -EINTR;

  	if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
  		__kthread_parkme(&self);
  		ret = threadfn(data);
  	}

  	/* we can't just return, we must preserve "self" on stack */
  	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);

  	}

  }

  /**

   * kthread_create_on_node - create a kthread.

   * @threadfn: the function to run until signal_pending(current).
   * @data: data ptr for @threadfn.

   * @node: memory node number.

   * @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().

   *

   * 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 -1.

   * 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).
   */

  struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),

  					   void *data, int node,

  					   const char namefmt[],
  					   ...)

  {

  	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(-ENOMEM);
  		/*
  		 * 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 };

  		va_list args;

  		va_start(args, namefmt);

  		vsnprintf(task->comm, sizeof(task->comm), namefmt, args);

  		va_end(args);

  		/*
  		 * 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;

  }

  EXPORT_SYMBOL(kthread_create_on_node);

  static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)

  {

  	/* Must have done schedule() in kthread() before we set_task_cpu */
  	if (!wait_task_inactive(p, state)) {
  		WARN_ON(1);
  		return;
  	}

  	/* It's safe because the task is inactive. */
  	do_set_cpus_allowed(p, cpumask_of(cpu));

  	p->flags |= PF_NO_SETAFFINITY;

  }

  /**

   * 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_mem(cpu), namefmt,

  				   cpu);
  	if (IS_ERR(p))
  		return p;
  	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
  	to_kthread(p)->cpu = cpu;
  	/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
  	kthread_park(p);
  	return p;
  }

  static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
  {
  	clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
  	/*
  	 * We clear the IS_PARKED bit here as we don't wait
  	 * until the task has left the park code. So if we'd
  	 * park before that happens we'd see the IS_PARKED bit
  	 * which might be about to be cleared.
  	 */
  	if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
  		if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
  			__kthread_bind(k, kthread->cpu, TASK_PARKED);
  		wake_up_state(k, TASK_PARKED);
  	}
  }

  /**
   * 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_live_kthread(k);

  	if (kthread)
  		__kthread_unpark(k, kthread);

  }
  
  /**
   * 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_live_kthread(k);

  	int ret = -ENOSYS;
  
  	if (kthread) {
  		if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
  			set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
  			if (k != current) {
  				wake_up_process(k);
  				wait_for_completion(&kthread->parked);
  			}
  		}
  		ret = 0;
  	}

  	return ret;
  }
  
  /**

   * 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_live_kthread(k);

  	if (kthread) {
  		set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);

  		__kthread_unpark(k, kthread);

  		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;

  
  	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 __init_kthread_worker(struct kthread_worker *worker,
  				const char *name,
  				struct lock_class_key *key)
  {
  	spin_lock_init(&worker->lock);
  	lockdep_set_class_and_name(&worker->lock, key, name);
  	INIT_LIST_HEAD(&worker->work_list);
  	worker->task = NULL;
  }
  EXPORT_SYMBOL_GPL(__init_kthread_worker);

  /**
   * kthread_worker_fn - kthread function to process kthread_worker
   * @worker_ptr: pointer to initialized kthread_worker
   *
   * This function can be used as @threadfn to kthread_create() or
   * kthread_run() with @worker_ptr argument pointing to an initialized
   * kthread_worker.  The started kthread will process work_list until
   * the it is stopped with kthread_stop().  A kthread can also call
   * this function directly after extra initialization.
   *
   * Different kthreads can be used for the same kthread_worker as long
   * as there's only one kthread attached to it at any given time.  A
   * kthread_worker without an attached kthread simply collects queued
   * kthread_works.
   */
  int kthread_worker_fn(void *worker_ptr)
  {
  	struct kthread_worker *worker = worker_ptr;
  	struct kthread_work *work;
  
  	WARN_ON(worker->task);
  	worker->task = current;
  repeat:
  	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
  
  	if (kthread_should_stop()) {
  		__set_current_state(TASK_RUNNING);
  		spin_lock_irq(&worker->lock);
  		worker->task = NULL;
  		spin_unlock_irq(&worker->lock);
  		return 0;
  	}
  
  	work = NULL;
  	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;

  	spin_unlock_irq(&worker->lock);
  
  	if (work) {
  		__set_current_state(TASK_RUNNING);
  		work->func(work);

  	} else if (!freezing(current))
  		schedule();
  
  	try_to_freeze();
  	goto repeat;
  }
  EXPORT_SYMBOL_GPL(kthread_worker_fn);

  /* insert @work before @pos in @worker */
  static void insert_kthread_work(struct kthread_worker *worker,
  			       struct kthread_work *work,
  			       struct list_head *pos)
  {
  	lockdep_assert_held(&worker->lock);
  
  	list_add_tail(&work->node, pos);

  	work->worker = worker;

  	if (likely(worker->task))
  		wake_up_process(worker->task);
  }

  /**
   * queue_kthread_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.
   */
  bool queue_kthread_work(struct kthread_worker *worker,
  			struct kthread_work *work)
  {
  	bool ret = false;
  	unsigned long flags;
  
  	spin_lock_irqsave(&worker->lock, flags);
  	if (list_empty(&work->node)) {

  		insert_kthread_work(worker, work, &worker->work_list);

  		ret = true;
  	}
  	spin_unlock_irqrestore(&worker->lock, flags);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(queue_kthread_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);
  }

  /**
   * flush_kthread_work - flush a kthread_work
   * @work: work to flush
   *
   * If @work is queued or executing, wait for it to finish execution.
   */
  void flush_kthread_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;
  
  retry:
  	worker = work->worker;
  	if (!worker)
  		return;

  	spin_lock_irq(&worker->lock);
  	if (work->worker != worker) {
  		spin_unlock_irq(&worker->lock);
  		goto retry;
  	}

  	if (!list_empty(&work->node))
  		insert_kthread_work(worker, &fwork.work, work->node.next);
  	else if (worker->current_work == work)
  		insert_kthread_work(worker, &fwork.work, worker->work_list.next);
  	else
  		noop = true;

  	spin_unlock_irq(&worker->lock);

  	if (!noop)
  		wait_for_completion(&fwork.done);

  }
  EXPORT_SYMBOL_GPL(flush_kthread_work);

  /**
   * flush_kthread_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 flush_kthread_worker(struct kthread_worker *worker)
  {
  	struct kthread_flush_work fwork = {
  		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
  		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
  	};
  
  	queue_kthread_work(worker, &fwork.work);
  	wait_for_completion(&fwork.done);
  }
  EXPORT_SYMBOL_GPL(flush_kthread_worker);