kernel/sched/completion.c - linux - Git at Google

 /*
  * Generic wait-for-completion handler;
  *
  * It differs from semaphores in that their default case is the opposite,
  * wait_for_completion default blocks whereas semaphore default non-block. The
  * interface also makes it easy to 'complete' multiple waiting threads,
  * something which isn't entirely natural for semaphores.
  *
  * But more importantly, the primitive documents the usage. Semaphores would
  * typically be used for exclusion which gives rise to priority inversion.
  * Waiting for completion is a typically sync point, but not an exclusion point.
  */

 #include <linux/sched.h>
 #include <linux/completion.h>

 /**
  * complete: - signals a single thread waiting on this completion
  * @x:  holds the state of this particular completion
  *
  * This will wake up a single thread waiting on this completion. Threads will be
  * awakened in the same order in which they were queued.
  *
  * See also complete_all(), wait_for_completion() and related routines.
  *
  * 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 complete(struct completion *x)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&x->wait.lock, flags);
 	x->done++;
 	__wake_up_locked(&x->wait, TASK_NORMAL, 1);
 	spin_unlock_irqrestore(&x->wait.lock, flags);
 }
 EXPORT_SYMBOL(complete);

 /**
  * complete_all: - signals all threads waiting on this completion
  * @x:  holds the state of this particular completion
  *
  * This will wake up all threads waiting on this particular completion event.
  *
  * 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 complete_all(struct completion *x)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&x->wait.lock, flags);
 	x->done += UINT_MAX/2;
 	__wake_up_locked(&x->wait, TASK_NORMAL, 0);
 	spin_unlock_irqrestore(&x->wait.lock, flags);
 }
 EXPORT_SYMBOL(complete_all);

 static inline long __sched
 do_wait_for_common(struct completion *x,
 		   long (*action)(long), long timeout, int state)
 {
 	if (!x->done) {
 		DECLARE_WAITQUEUE(wait, current);

 		__add_wait_queue_tail_exclusive(&x->wait, &wait);
 		do {
 			if (signal_pending_state(state, current)) {
 				timeout = -ERESTARTSYS;
 				break;
 			}
 			__set_current_state(state);
 			spin_unlock_irq(&x->wait.lock);
 			timeout = action(timeout);
 			spin_lock_irq(&x->wait.lock);
 		} while (!x->done && timeout);
 		__remove_wait_queue(&x->wait, &wait);
 		if (!x->done)
 			return timeout;
 	}
 	x->done--;
 	return timeout ?: 1;
 }

 static inline long __sched
 __wait_for_common(struct completion *x,
 		  long (*action)(long), long timeout, int state)
 {
 	might_sleep();

 	spin_lock_irq(&x->wait.lock);
 	timeout = do_wait_for_common(x, action, timeout, state);
 	spin_unlock_irq(&x->wait.lock);
 	return timeout;
 }

 static long __sched
 wait_for_common(struct completion *x, long timeout, int state)
 {
 	return __wait_for_common(x, schedule_timeout, timeout, state);
 }

 static long __sched
 wait_for_common_io(struct completion *x, long timeout, int state)
 {
 	return __wait_for_common(x, io_schedule_timeout, timeout, state);
 }

 /**
  * wait_for_completion: - waits for completion of a task
  * @x:  holds the state of this particular completion
  *
  * This waits to be signaled for completion of a specific task. It is NOT
  * interruptible and there is no timeout.
  *
  * See also similar routines (i.e. wait_for_completion_timeout()) with timeout
  * and interrupt capability. Also see complete().
  */
 void __sched wait_for_completion(struct completion *x)
 {
 	wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_for_completion);

 /**
  * wait_for_completion_timeout: - waits for completion of a task (w/timeout)
  * @x:  holds the state of this particular completion
  * @timeout:  timeout value in jiffies
  *
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. The timeout is in jiffies. It is not
  * interruptible.
  *
  * Return: 0 if timed out, and positive (at least 1, or number of jiffies left
  * till timeout) if completed.
  */
 unsigned long __sched
 wait_for_completion_timeout(struct completion *x, unsigned long timeout)
 {
 	return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_for_completion_timeout);

 /**
  * wait_for_completion_io: - waits for completion of a task
  * @x:  holds the state of this particular completion
  *
  * This waits to be signaled for completion of a specific task. It is NOT
  * interruptible and there is no timeout. The caller is accounted as waiting
  * for IO (which traditionally means blkio only).
  */
 void __sched wait_for_completion_io(struct completion *x)
 {
 	wait_for_common_io(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_for_completion_io);

 /**
  * wait_for_completion_io_timeout: - waits for completion of a task (w/timeout)
  * @x:  holds the state of this particular completion
  * @timeout:  timeout value in jiffies
  *
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. The timeout is in jiffies. It is not
  * interruptible. The caller is accounted as waiting for IO (which traditionally
  * means blkio only).
  *
  * Return: 0 if timed out, and positive (at least 1, or number of jiffies left
  * till timeout) if completed.
  */
 unsigned long __sched
 wait_for_completion_io_timeout(struct completion *x, unsigned long timeout)
 {
 	return wait_for_common_io(x, timeout, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_for_completion_io_timeout);

 /**
  * wait_for_completion_interruptible: - waits for completion of a task (w/intr)
  * @x:  holds the state of this particular completion
  *
  * This waits for completion of a specific task to be signaled. It is
  * interruptible.
  *
  * Return: -ERESTARTSYS if interrupted, 0 if completed.
  */
 int __sched wait_for_completion_interruptible(struct completion *x)
 {
 	long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
 	if (t == -ERESTARTSYS)
 		return t;
 	return 0;
 }
 EXPORT_SYMBOL(wait_for_completion_interruptible);

 /**
  * wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr))
  * @x:  holds the state of this particular completion
  * @timeout:  timeout value in jiffies
  *
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. It is interruptible. The timeout is in jiffies.
  *
  * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
  * or number of jiffies left till timeout) if completed.
  */
 long __sched
 wait_for_completion_interruptible_timeout(struct completion *x,
 					  unsigned long timeout)
 {
 	return wait_for_common(x, timeout, TASK_INTERRUPTIBLE);
 }
 EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);

 /**
  * wait_for_completion_killable: - waits for completion of a task (killable)
  * @x:  holds the state of this particular completion
  *
  * This waits to be signaled for completion of a specific task. It can be
  * interrupted by a kill signal.
  *
  * Return: -ERESTARTSYS if interrupted, 0 if completed.
  */
 int __sched wait_for_completion_killable(struct completion *x)
 {
 	long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_KILLABLE);
 	if (t == -ERESTARTSYS)
 		return t;
 	return 0;
 }
 EXPORT_SYMBOL(wait_for_completion_killable);

 /**
  * wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
  * @x:  holds the state of this particular completion
  * @timeout:  timeout value in jiffies
  *
  * This waits for either a completion of a specific task to be
  * signaled or for a specified timeout to expire. It can be
  * interrupted by a kill signal. The timeout is in jiffies.
  *
  * Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
  * or number of jiffies left till timeout) if completed.
  */
 long __sched
 wait_for_completion_killable_timeout(struct completion *x,
 				     unsigned long timeout)
 {
 	return wait_for_common(x, timeout, TASK_KILLABLE);
 }
 EXPORT_SYMBOL(wait_for_completion_killable_timeout);

 /**
  *	try_wait_for_completion - try to decrement a completion without blocking
  *	@x:	completion structure
  *
  *	Return: 0 if a decrement cannot be done without blocking
  *		 1 if a decrement succeeded.
  *
  *	If a completion is being used as a counting completion,
  *	attempt to decrement the counter without blocking. This
  *	enables us to avoid waiting if the resource the completion
  *	is protecting is not available.
  */
 bool try_wait_for_completion(struct completion *x)
 {
 	unsigned long flags;
 	int ret = 1;

 	/*
 	 * Since x->done will need to be locked only
 	 * in the non-blocking case, we check x->done
 	 * first without taking the lock so we can
 	 * return early in the blocking case.
 	 */
 	if (!READ_ONCE(x->done))
 		return 0;

 	spin_lock_irqsave(&x->wait.lock, flags);
 	if (!x->done)
 		ret = 0;
 	else
 		x->done--;
 	spin_unlock_irqrestore(&x->wait.lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL(try_wait_for_completion);

 /**
  *	completion_done - Test to see if a completion has any waiters
  *	@x:	completion structure
  *
  *	Return: 0 if there are waiters (wait_for_completion() in progress)
  *		 1 if there are no waiters.
  *
  */
 bool completion_done(struct completion *x)
 {
 	if (!READ_ONCE(x->done))
 		return false;

 	/*
 	 * If ->done, we need to wait for complete() to release ->wait.lock
 	 * otherwise we can end up freeing the completion before complete()
 	 * is done referencing it.
 	 *
 	 * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
 	 * the loads of ->done and ->wait.lock such that we cannot observe
 	 * the lock before complete() acquires it while observing the ->done
 	 * after it's acquired the lock.
 	 */
 	smp_rmb();
 	spin_unlock_wait(&x->wait.lock);
 	return true;
 }
 EXPORT_SYMBOL(completion_done);
	/*
	* Generic wait-for-completion handler;
	*
	* It differs from semaphores in that their default case is the opposite,
	* wait_for_completion default blocks whereas semaphore default non-block. The
	* interface also makes it easy to 'complete' multiple waiting threads,
	* something which isn't entirely natural for semaphores.
	*
	* But more importantly, the primitive documents the usage. Semaphores would
	* typically be used for exclusion which gives rise to priority inversion.
	* Waiting for completion is a typically sync point, but not an exclusion point.
	*/

	#include <linux/sched.h>
	#include <linux/completion.h>

	/**
	* complete: - signals a single thread waiting on this completion
	* @x: holds the state of this particular completion
	*
	* This will wake up a single thread waiting on this completion. Threads will be
	* awakened in the same order in which they were queued.
	*
	* See also complete_all(), wait_for_completion() and related routines.
	*
	* 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 complete(struct completion *x)
	{
	unsigned long flags;

	spin_lock_irqsave(&x->wait.lock, flags);
	x->done++;
	__wake_up_locked(&x->wait, TASK_NORMAL, 1);
	spin_unlock_irqrestore(&x->wait.lock, flags);
	}
	EXPORT_SYMBOL(complete);

	/**
	* complete_all: - signals all threads waiting on this completion
	* @x: holds the state of this particular completion
	*
	* This will wake up all threads waiting on this particular completion event.
	*
	* 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 complete_all(struct completion *x)
	{
	unsigned long flags;

	spin_lock_irqsave(&x->wait.lock, flags);
	x->done += UINT_MAX/2;
	__wake_up_locked(&x->wait, TASK_NORMAL, 0);
	spin_unlock_irqrestore(&x->wait.lock, flags);
	}
	EXPORT_SYMBOL(complete_all);

	static inline long __sched
	do_wait_for_common(struct completion *x,
	long (*action)(long), long timeout, int state)
	{
	if (!x->done) {
	DECLARE_WAITQUEUE(wait, current);

	__add_wait_queue_tail_exclusive(&x->wait, &wait);
	do {
	if (signal_pending_state(state, current)) {
	timeout = -ERESTARTSYS;
	break;
	}
	__set_current_state(state);
	spin_unlock_irq(&x->wait.lock);
	timeout = action(timeout);
	spin_lock_irq(&x->wait.lock);
	} while (!x->done && timeout);
	__remove_wait_queue(&x->wait, &wait);
	if (!x->done)
	return timeout;
	}
	x->done--;
	return timeout ?: 1;
	}

	static inline long __sched
	__wait_for_common(struct completion *x,
	long (*action)(long), long timeout, int state)
	{
	might_sleep();

	spin_lock_irq(&x->wait.lock);
	timeout = do_wait_for_common(x, action, timeout, state);
	spin_unlock_irq(&x->wait.lock);
	return timeout;
	}

	static long __sched
	wait_for_common(struct completion *x, long timeout, int state)
	{
	return __wait_for_common(x, schedule_timeout, timeout, state);
	}

	static long __sched
	wait_for_common_io(struct completion *x, long timeout, int state)
	{
	return __wait_for_common(x, io_schedule_timeout, timeout, state);
	}

	/**
	* wait_for_completion: - waits for completion of a task
	* @x: holds the state of this particular completion
	*
	* This waits to be signaled for completion of a specific task. It is NOT
	* interruptible and there is no timeout.
	*
	* See also similar routines (i.e. wait_for_completion_timeout()) with timeout
	* and interrupt capability. Also see complete().
	*/
	void __sched wait_for_completion(struct completion *x)
	{
	wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
	}
	EXPORT_SYMBOL(wait_for_completion);

	/**
	* wait_for_completion_timeout: - waits for completion of a task (w/timeout)
	* @x: holds the state of this particular completion
	* @timeout: timeout value in jiffies
	*
	* This waits for either a completion of a specific task to be signaled or for a
	* specified timeout to expire. The timeout is in jiffies. It is not
	* interruptible.
	*
	* Return: 0 if timed out, and positive (at least 1, or number of jiffies left
	* till timeout) if completed.
	*/
	unsigned long __sched
	wait_for_completion_timeout(struct completion *x, unsigned long timeout)
	{
	return wait_for_common(x, timeout, TASK_UNINTERRUPTIBLE);
	}
	EXPORT_SYMBOL(wait_for_completion_timeout);

	/**
	* wait_for_completion_io: - waits for completion of a task
	* @x: holds the state of this particular completion
	*
	* This waits to be signaled for completion of a specific task. It is NOT
	* interruptible and there is no timeout. The caller is accounted as waiting
	* for IO (which traditionally means blkio only).
	*/
	void __sched wait_for_completion_io(struct completion *x)
	{
	wait_for_common_io(x, MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
	}
	EXPORT_SYMBOL(wait_for_completion_io);

	/**
	* wait_for_completion_io_timeout: - waits for completion of a task (w/timeout)
	* @x: holds the state of this particular completion
	* @timeout: timeout value in jiffies
	*
	* This waits for either a completion of a specific task to be signaled or for a
	* specified timeout to expire. The timeout is in jiffies. It is not
	* interruptible. The caller is accounted as waiting for IO (which traditionally
	* means blkio only).
	*
	* Return: 0 if timed out, and positive (at least 1, or number of jiffies left
	* till timeout) if completed.
	*/
	unsigned long __sched
	wait_for_completion_io_timeout(struct completion *x, unsigned long timeout)
	{
	return wait_for_common_io(x, timeout, TASK_UNINTERRUPTIBLE);
	}
	EXPORT_SYMBOL(wait_for_completion_io_timeout);

	/**
	* wait_for_completion_interruptible: - waits for completion of a task (w/intr)
	* @x: holds the state of this particular completion
	*
	* This waits for completion of a specific task to be signaled. It is
	* interruptible.
	*
	* Return: -ERESTARTSYS if interrupted, 0 if completed.
	*/
	int __sched wait_for_completion_interruptible(struct completion *x)
	{
	long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
	if (t == -ERESTARTSYS)
	return t;
	return 0;
	}
	EXPORT_SYMBOL(wait_for_completion_interruptible);

	/**
	* wait_for_completion_interruptible_timeout: - waits for completion (w/(to,intr))
	* @x: holds the state of this particular completion
	* @timeout: timeout value in jiffies
	*
	* This waits for either a completion of a specific task to be signaled or for a
	* specified timeout to expire. It is interruptible. The timeout is in jiffies.
	*
	* Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
	* or number of jiffies left till timeout) if completed.
	*/
	long __sched
	wait_for_completion_interruptible_timeout(struct completion *x,
	unsigned long timeout)
	{
	return wait_for_common(x, timeout, TASK_INTERRUPTIBLE);
	}
	EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);

	/**
	* wait_for_completion_killable: - waits for completion of a task (killable)
	* @x: holds the state of this particular completion
	*
	* This waits to be signaled for completion of a specific task. It can be
	* interrupted by a kill signal.
	*
	* Return: -ERESTARTSYS if interrupted, 0 if completed.
	*/
	int __sched wait_for_completion_killable(struct completion *x)
	{
	long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_KILLABLE);
	if (t == -ERESTARTSYS)
	return t;
	return 0;
	}
	EXPORT_SYMBOL(wait_for_completion_killable);

	/**
	* wait_for_completion_killable_timeout: - waits for completion of a task (w/(to,killable))
	* @x: holds the state of this particular completion
	* @timeout: timeout value in jiffies
	*
	* This waits for either a completion of a specific task to be
	* signaled or for a specified timeout to expire. It can be
	* interrupted by a kill signal. The timeout is in jiffies.
	*
	* Return: -ERESTARTSYS if interrupted, 0 if timed out, positive (at least 1,
	* or number of jiffies left till timeout) if completed.
	*/
	long __sched
	wait_for_completion_killable_timeout(struct completion *x,
	unsigned long timeout)
	{
	return wait_for_common(x, timeout, TASK_KILLABLE);
	}
	EXPORT_SYMBOL(wait_for_completion_killable_timeout);

	/**
	* try_wait_for_completion - try to decrement a completion without blocking
	* @x: completion structure
	*
	* Return: 0 if a decrement cannot be done without blocking
	* 1 if a decrement succeeded.
	*
	* If a completion is being used as a counting completion,
	* attempt to decrement the counter without blocking. This
	* enables us to avoid waiting if the resource the completion
	* is protecting is not available.
	*/
	bool try_wait_for_completion(struct completion *x)
	{
	unsigned long flags;
	int ret = 1;

	/*
	* Since x->done will need to be locked only
	* in the non-blocking case, we check x->done
	* first without taking the lock so we can
	* return early in the blocking case.
	*/
	if (!READ_ONCE(x->done))
	return 0;

	spin_lock_irqsave(&x->wait.lock, flags);
	if (!x->done)
	ret = 0;
	else
	x->done--;
	spin_unlock_irqrestore(&x->wait.lock, flags);
	return ret;
	}
	EXPORT_SYMBOL(try_wait_for_completion);

	/**
	* completion_done - Test to see if a completion has any waiters
	* @x: completion structure
	*
	* Return: 0 if there are waiters (wait_for_completion() in progress)
	* 1 if there are no waiters.
	*
	*/
	bool completion_done(struct completion *x)
	{
	if (!READ_ONCE(x->done))
	return false;

	/*
	* If ->done, we need to wait for complete() to release ->wait.lock
	* otherwise we can end up freeing the completion before complete()
	* is done referencing it.
	*
	* The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
	* the loads of ->done and ->wait.lock such that we cannot observe
	* the lock before complete() acquires it while observing the ->done
	* after it's acquired the lock.
	*/
	smp_rmb();
	spin_unlock_wait(&x->wait.lock);
	return true;
	}
	EXPORT_SYMBOL(completion_done);