/*
   * Generic waiting primitives.
   *

   * (C) 2004 Nadia Yvette Chambers, Oracle

   */

  #include <linux/init.h>

  #include <linux/export.h>

  #include <linux/sched.h>
  #include <linux/mm.h>
  #include <linux/wait.h>
  #include <linux/hash.h>

  #include <linux/kthread.h>

  void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)

  {
  	spin_lock_init(&q->lock);

  	lockdep_set_class_and_name(&q->lock, key, name);

  	INIT_LIST_HEAD(&q->task_list);
  }

  EXPORT_SYMBOL(__init_waitqueue_head);

  void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	__add_wait_queue(q, wait);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(add_wait_queue);

  void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	wait->flags |= WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	__add_wait_queue_tail(q, wait);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(add_wait_queue_exclusive);

  void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&q->lock, flags);
  	__remove_wait_queue(q, wait);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(remove_wait_queue);
  
  
  /*

   * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
   * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
   * number) then we wake all the non-exclusive tasks and one exclusive task.
   *
   * There are circumstances in which we can try to wake a task which has already
   * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
   * zero in this (rare) case, and we handle it by continuing to scan the queue.
   */
  static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
  			int nr_exclusive, int wake_flags, void *key)
  {
  	wait_queue_t *curr, *next;
  
  	list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
  		unsigned flags = curr->flags;
  
  		if (curr->func(curr, mode, wake_flags, key) &&
  				(flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
  			break;
  	}
  }
  
  /**
   * __wake_up - wake up threads blocked on a waitqueue.
   * @q: the waitqueue
   * @mode: which threads
   * @nr_exclusive: how many wake-one or wake-many threads to wake up
   * @key: is directly passed to the wakeup function
   *
   * It may be assumed that this function implies a write memory barrier before
   * changing the task state if and only if any tasks are woken up.
   */
  void __wake_up(wait_queue_head_t *q, unsigned int mode,
  			int nr_exclusive, void *key)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&q->lock, flags);
  	__wake_up_common(q, mode, nr_exclusive, 0, key);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(__wake_up);
  
  /*
   * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
   */
  void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
  {
  	__wake_up_common(q, mode, nr, 0, NULL);
  }
  EXPORT_SYMBOL_GPL(__wake_up_locked);
  
  void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
  {
  	__wake_up_common(q, mode, 1, 0, key);
  }
  EXPORT_SYMBOL_GPL(__wake_up_locked_key);
  
  /**
   * __wake_up_sync_key - wake up threads blocked on a waitqueue.
   * @q: the waitqueue
   * @mode: which threads
   * @nr_exclusive: how many wake-one or wake-many threads to wake up
   * @key: opaque value to be passed to wakeup targets
   *
   * The sync wakeup differs that the waker knows that it will schedule
   * away soon, so while the target thread will be woken up, it will not
   * be migrated to another CPU - ie. the two threads are 'synchronized'
   * with each other. This can prevent needless bouncing between CPUs.
   *
   * On UP it can prevent extra preemption.
   *
   * It may be assumed that this function implies a write memory barrier before
   * changing the task state if and only if any tasks are woken up.
   */
  void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
  			int nr_exclusive, void *key)
  {
  	unsigned long flags;
  	int wake_flags = 1; /* XXX WF_SYNC */
  
  	if (unlikely(!q))
  		return;
  
  	if (unlikely(nr_exclusive != 1))
  		wake_flags = 0;
  
  	spin_lock_irqsave(&q->lock, flags);
  	__wake_up_common(q, mode, nr_exclusive, wake_flags, key);
  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL_GPL(__wake_up_sync_key);
  
  /*
   * __wake_up_sync - see __wake_up_sync_key()
   */
  void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
  {
  	__wake_up_sync_key(q, mode, nr_exclusive, NULL);
  }
  EXPORT_SYMBOL_GPL(__wake_up_sync);	/* For internal use only */
  
  /*

   * Note: we use "set_current_state()" _after_ the wait-queue add,
   * because we need a memory barrier there on SMP, so that any
   * wake-function that tests for the wait-queue being active
   * will be guaranteed to see waitqueue addition _or_ subsequent
   * tests in this thread will see the wakeup having taken place.
   *
   * The spin_unlock() itself is semi-permeable and only protects
   * one way (it only protects stuff inside the critical region and
   * stops them from bleeding out - it would still allow subsequent

   * loads to move into the critical region).

   */

  void

  prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
  {
  	unsigned long flags;
  
  	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	if (list_empty(&wait->task_list))
  		__add_wait_queue(q, wait);

  	set_current_state(state);

  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(prepare_to_wait);

  void

  prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
  {
  	unsigned long flags;
  
  	wait->flags |= WQ_FLAG_EXCLUSIVE;
  	spin_lock_irqsave(&q->lock, flags);
  	if (list_empty(&wait->task_list))
  		__add_wait_queue_tail(q, wait);

  	set_current_state(state);

  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(prepare_to_wait_exclusive);

  long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
  {
  	unsigned long flags;
  
  	if (signal_pending_state(state, current))
  		return -ERESTARTSYS;
  
  	wait->private = current;
  	wait->func = autoremove_wake_function;
  
  	spin_lock_irqsave(&q->lock, flags);
  	if (list_empty(&wait->task_list)) {
  		if (wait->flags & WQ_FLAG_EXCLUSIVE)
  			__add_wait_queue_tail(q, wait);
  		else
  			__add_wait_queue(q, wait);
  	}
  	set_current_state(state);
  	spin_unlock_irqrestore(&q->lock, flags);
  
  	return 0;
  }
  EXPORT_SYMBOL(prepare_to_wait_event);

  /**

   * finish_wait - clean up after waiting in a queue
   * @q: waitqueue waited on
   * @wait: wait descriptor
   *
   * Sets current thread back to running state and removes
   * the wait descriptor from the given waitqueue if still
   * queued.
   */

  void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)

  {
  	unsigned long flags;
  
  	__set_current_state(TASK_RUNNING);
  	/*
  	 * We can check for list emptiness outside the lock
  	 * IFF:
  	 *  - we use the "careful" check that verifies both
  	 *    the next and prev pointers, so that there cannot
  	 *    be any half-pending updates in progress on other
  	 *    CPU's that we haven't seen yet (and that might
  	 *    still change the stack area.
  	 * and
  	 *  - all other users take the lock (ie we can only
  	 *    have _one_ other CPU that looks at or modifies
  	 *    the list).
  	 */
  	if (!list_empty_careful(&wait->task_list)) {
  		spin_lock_irqsave(&q->lock, flags);
  		list_del_init(&wait->task_list);
  		spin_unlock_irqrestore(&q->lock, flags);
  	}
  }
  EXPORT_SYMBOL(finish_wait);

  /**

   * abort_exclusive_wait - abort exclusive waiting in a queue
   * @q: waitqueue waited on
   * @wait: wait descriptor

   * @mode: runstate of the waiter to be woken

   * @key: key to identify a wait bit queue or %NULL
   *
   * Sets current thread back to running state and removes
   * the wait descriptor from the given waitqueue if still
   * queued.
   *
   * Wakes up the next waiter if the caller is concurrently
   * woken up through the queue.
   *
   * This prevents waiter starvation where an exclusive waiter

   * aborts and is woken up concurrently and no one wakes up

   * the next waiter.
   */
  void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
  			unsigned int mode, void *key)
  {
  	unsigned long flags;
  
  	__set_current_state(TASK_RUNNING);
  	spin_lock_irqsave(&q->lock, flags);
  	if (!list_empty(&wait->task_list))
  		list_del_init(&wait->task_list);
  	else if (waitqueue_active(q))

  		__wake_up_locked_key(q, mode, key);

  	spin_unlock_irqrestore(&q->lock, flags);
  }
  EXPORT_SYMBOL(abort_exclusive_wait);

  int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
  {
  	int ret = default_wake_function(wait, mode, sync, key);
  
  	if (ret)
  		list_del_init(&wait->task_list);
  	return ret;
  }
  EXPORT_SYMBOL(autoremove_wake_function);

  static inline bool is_kthread_should_stop(void)
  {
  	return (current->flags & PF_KTHREAD) && kthread_should_stop();
  }

  
  /*
   * DEFINE_WAIT_FUNC(wait, woken_wake_func);
   *
   * add_wait_queue(&wq, &wait);
   * for (;;) {
   *     if (condition)
   *         break;
   *
   *     p->state = mode;				condition = true;
   *     smp_mb(); // A				smp_wmb(); // C
   *     if (!wait->flags & WQ_FLAG_WOKEN)	wait->flags |= WQ_FLAG_WOKEN;
   *         schedule()				try_to_wake_up();
   *     p->state = TASK_RUNNING;		    ~~~~~~~~~~~~~~~~~~
   *     wait->flags &= ~WQ_FLAG_WOKEN;		condition = true;
   *     smp_mb() // B				smp_wmb(); // C
   *						wait->flags |= WQ_FLAG_WOKEN;
   * }
   * remove_wait_queue(&wq, &wait);
   *
   */
  long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
  {
  	set_current_state(mode); /* A */
  	/*
  	 * The above implies an smp_mb(), which matches with the smp_wmb() from
  	 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
  	 * also observe all state before the wakeup.
  	 */

  	if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())

  		timeout = schedule_timeout(timeout);
  	__set_current_state(TASK_RUNNING);
  
  	/*
  	 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
  	 * woken_wake_function() such that we must either observe the wait
  	 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
  	 * an event.
  	 */
  	set_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */
  
  	return timeout;
  }
  EXPORT_SYMBOL(wait_woken);
  
  int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
  {
  	/*
  	 * Although this function is called under waitqueue lock, LOCK
  	 * doesn't imply write barrier and the users expects write
  	 * barrier semantics on wakeup functions.  The following
  	 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
  	 * and is paired with set_mb() in wait_woken().
  	 */
  	smp_wmb(); /* C */
  	wait->flags |= WQ_FLAG_WOKEN;
  
  	return default_wake_function(wait, mode, sync, key);
  }
  EXPORT_SYMBOL(woken_wake_function);

  int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
  {
  	struct wait_bit_key *key = arg;
  	struct wait_bit_queue *wait_bit
  		= container_of(wait, struct wait_bit_queue, wait);
  
  	if (wait_bit->key.flags != key->flags ||
  			wait_bit->key.bit_nr != key->bit_nr ||
  			test_bit(key->bit_nr, key->flags))
  		return 0;
  	else
  		return autoremove_wake_function(wait, mode, sync, key);
  }
  EXPORT_SYMBOL(wake_bit_function);
  
  /*
   * To allow interruptible waiting and asynchronous (i.e. nonblocking)
   * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
   * permitted return codes. Nonzero return codes halt waiting and return.
   */

  int __sched

  __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,

  	      wait_bit_action_f *action, unsigned mode)

  {
  	int ret = 0;
  
  	do {
  		prepare_to_wait(wq, &q->wait, mode);
  		if (test_bit(q->key.bit_nr, q->key.flags))

  			ret = (*action)(&q->key);

  	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
  	finish_wait(wq, &q->wait);
  	return ret;
  }
  EXPORT_SYMBOL(__wait_on_bit);

  int __sched out_of_line_wait_on_bit(void *word, int bit,

  				    wait_bit_action_f *action, unsigned mode)

  {
  	wait_queue_head_t *wq = bit_waitqueue(word, bit);
  	DEFINE_WAIT_BIT(wait, word, bit);
  
  	return __wait_on_bit(wq, &wait, action, mode);
  }
  EXPORT_SYMBOL(out_of_line_wait_on_bit);

  int __sched out_of_line_wait_on_bit_timeout(
  	void *word, int bit, wait_bit_action_f *action,
  	unsigned mode, unsigned long timeout)
  {
  	wait_queue_head_t *wq = bit_waitqueue(word, bit);
  	DEFINE_WAIT_BIT(wait, word, bit);
  
  	wait.key.timeout = jiffies + timeout;
  	return __wait_on_bit(wq, &wait, action, mode);
  }
  EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);

  int __sched

  __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,

  			wait_bit_action_f *action, unsigned mode)

  {

  	do {

  		int ret;

  		prepare_to_wait_exclusive(wq, &q->wait, mode);

  		if (!test_bit(q->key.bit_nr, q->key.flags))
  			continue;

  		ret = action(&q->key);

  		if (!ret)
  			continue;
  		abort_exclusive_wait(wq, &q->wait, mode, &q->key);
  		return ret;

  	} while (test_and_set_bit(q->key.bit_nr, q->key.flags));
  	finish_wait(wq, &q->wait);

  	return 0;

  }
  EXPORT_SYMBOL(__wait_on_bit_lock);

  int __sched out_of_line_wait_on_bit_lock(void *word, int bit,

  					 wait_bit_action_f *action, unsigned mode)

  {
  	wait_queue_head_t *wq = bit_waitqueue(word, bit);
  	DEFINE_WAIT_BIT(wait, word, bit);
  
  	return __wait_on_bit_lock(wq, &wait, action, mode);
  }
  EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);

  void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)

  {
  	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
  	if (waitqueue_active(wq))

  		__wake_up(wq, TASK_NORMAL, 1, &key);

  }
  EXPORT_SYMBOL(__wake_up_bit);
  
  /**
   * wake_up_bit - wake up a waiter on a bit
   * @word: the word being waited on, a kernel virtual address
   * @bit: the bit of the word being waited on
   *
   * There is a standard hashed waitqueue table for generic use. This
   * is the part of the hashtable's accessor API that wakes up waiters
   * on a bit. For instance, if one were to have waiters on a bitflag,
   * one would call wake_up_bit() after clearing the bit.
   *
   * In order for this to function properly, as it uses waitqueue_active()
   * internally, some kind of memory barrier must be done prior to calling

   * this. Typically, this will be smp_mb__after_atomic(), but in some

   * cases where bitflags are manipulated non-atomically under a lock, one
   * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
   * because spin_unlock() does not guarantee a memory barrier.
   */

  void wake_up_bit(void *word, int bit)

  {
  	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
  }
  EXPORT_SYMBOL(wake_up_bit);

  wait_queue_head_t *bit_waitqueue(void *word, int bit)

  {
  	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
  	const struct zone *zone = page_zone(virt_to_page(word));
  	unsigned long val = (unsigned long)word << shift | bit;
  
  	return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
  }
  EXPORT_SYMBOL(bit_waitqueue);

  
  /*
   * Manipulate the atomic_t address to produce a better bit waitqueue table hash
   * index (we're keying off bit -1, but that would produce a horrible hash
   * value).
   */
  static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
  {
  	if (BITS_PER_LONG == 64) {
  		unsigned long q = (unsigned long)p;
  		return bit_waitqueue((void *)(q & ~1), q & 1);
  	}
  	return bit_waitqueue(p, 0);
  }
  
  static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
  				  void *arg)
  {
  	struct wait_bit_key *key = arg;
  	struct wait_bit_queue *wait_bit
  		= container_of(wait, struct wait_bit_queue, wait);
  	atomic_t *val = key->flags;
  
  	if (wait_bit->key.flags != key->flags ||
  	    wait_bit->key.bit_nr != key->bit_nr ||
  	    atomic_read(val) != 0)
  		return 0;
  	return autoremove_wake_function(wait, mode, sync, key);
  }
  
  /*
   * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
   * the actions of __wait_on_atomic_t() are permitted return codes.  Nonzero
   * return codes halt waiting and return.
   */
  static __sched
  int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
  		       int (*action)(atomic_t *), unsigned mode)
  {
  	atomic_t *val;
  	int ret = 0;
  
  	do {
  		prepare_to_wait(wq, &q->wait, mode);
  		val = q->key.flags;
  		if (atomic_read(val) == 0)

  			break;
  		ret = (*action)(val);

  	} while (!ret && atomic_read(val) != 0);
  	finish_wait(wq, &q->wait);
  	return ret;
  }
  
  #define DEFINE_WAIT_ATOMIC_T(name, p)					\
  	struct wait_bit_queue name = {					\
  		.key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),		\
  		.wait	= {						\
  			.private	= current,			\
  			.func		= wake_atomic_t_function,	\
  			.task_list	=				\
  				LIST_HEAD_INIT((name).wait.task_list),	\
  		},							\
  	}
  
  __sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
  					 unsigned mode)
  {
  	wait_queue_head_t *wq = atomic_t_waitqueue(p);
  	DEFINE_WAIT_ATOMIC_T(wait, p);
  
  	return __wait_on_atomic_t(wq, &wait, action, mode);
  }
  EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
  
  /**
   * wake_up_atomic_t - Wake up a waiter on a atomic_t

   * @p: The atomic_t being waited on, a kernel virtual address

   *
   * Wake up anyone waiting for the atomic_t to go to zero.
   *
   * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
   * check is done by the waiter's wake function, not the by the waker itself).
   */
  void wake_up_atomic_t(atomic_t *p)
  {
  	__wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
  }
  EXPORT_SYMBOL(wake_up_atomic_t);

  __sched int bit_wait(struct wait_bit_key *word)

  {
  	if (signal_pending_state(current->state, current))
  		return 1;
  	schedule();
  	return 0;
  }
  EXPORT_SYMBOL(bit_wait);

  __sched int bit_wait_io(struct wait_bit_key *word)

  {
  	if (signal_pending_state(current->state, current))
  		return 1;
  	io_schedule();
  	return 0;
  }
  EXPORT_SYMBOL(bit_wait_io);

  
  __sched int bit_wait_timeout(struct wait_bit_key *word)
  {
  	unsigned long now = ACCESS_ONCE(jiffies);
  	if (signal_pending_state(current->state, current))
  		return 1;
  	if (time_after_eq(now, word->timeout))
  		return -EAGAIN;
  	schedule_timeout(word->timeout - now);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(bit_wait_timeout);
  
  __sched int bit_wait_io_timeout(struct wait_bit_key *word)
  {
  	unsigned long now = ACCESS_ONCE(jiffies);
  	if (signal_pending_state(current->state, current))
  		return 1;
  	if (time_after_eq(now, word->timeout))
  		return -EAGAIN;
  	io_schedule_timeout(word->timeout - now);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(bit_wait_io_timeout);