/* * Generic waiting primitives. * * (C) 2004 Nadia Yvette Chambers, Oracle */#include <linux/init.h>#include <linux/export.h>#include <linux/sched/signal.h>#include <linux/sched/debug.h>#include <linux/mm.h>#include <linux/wait.h>#include <linux/hash.h>#include <linux/kthread.h> void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key){	spin_lock_init(&wq_head->lock);	lockdep_set_class_and_name(&wq_head->lock, key, name);	INIT_LIST_HEAD(&wq_head->head);} EXPORT_SYMBOL(__init_waitqueue_head); void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry){	unsigned long flags; 	wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;	spin_lock_irqsave(&wq_head->lock, flags);	__add_wait_queue_entry_tail(wq_head, wq_entry);	spin_unlock_irqrestore(&wq_head->lock, flags);}EXPORT_SYMBOL(add_wait_queue); void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry){	unsigned long flags; 	wq_entry->flags |= WQ_FLAG_EXCLUSIVE;	spin_lock_irqsave(&wq_head->lock, flags);	__add_wait_queue_entry_tail(wq_head, wq_entry);	spin_unlock_irqrestore(&wq_head->lock, flags);}EXPORT_SYMBOL(add_wait_queue_exclusive); void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry){	unsigned long flags; 	spin_lock_irqsave(&wq_head->lock, flags);	__remove_wait_queue(wq_head, wq_entry);	spin_unlock_irqrestore(&wq_head->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(struct wait_queue_head *wq_head, unsigned int mode,			int nr_exclusive, int wake_flags, void *key){	wait_queue_entry_t *curr, *next; 	list_for_each_entry_safe(curr, next, &wq_head->head, entry) {		unsigned flags = curr->flags;		int ret = curr->func(curr, mode, wake_flags, key);		if (ret < 0)			break;		if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)			break;	}} /** * __wake_up - wake up threads blocked on a waitqueue. * @wq_head: 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(struct wait_queue_head *wq_head, unsigned int mode,			int nr_exclusive, void *key){	unsigned long flags; 	spin_lock_irqsave(&wq_head->lock, flags);	__wake_up_common(wq_head, mode, nr_exclusive, 0, key);	spin_unlock_irqrestore(&wq_head->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(struct wait_queue_head *wq_head, unsigned int mode, int nr){	__wake_up_common(wq_head, mode, nr, 0, NULL);}EXPORT_SYMBOL_GPL(__wake_up_locked); void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key){	__wake_up_common(wq_head, mode, 1, 0, key);}EXPORT_SYMBOL_GPL(__wake_up_locked_key); /** * __wake_up_sync_key - wake up threads blocked on a waitqueue. * @wq_head: 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(struct wait_queue_head *wq_head, unsigned int mode,			int nr_exclusive, void *key){	unsigned long flags;	int wake_flags = 1; /* XXX WF_SYNC */ 	if (unlikely(!wq_head))		return; 	if (unlikely(nr_exclusive != 1))		wake_flags = 0; 	spin_lock_irqsave(&wq_head->lock, flags);	__wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key);	spin_unlock_irqrestore(&wq_head->lock, flags);}EXPORT_SYMBOL_GPL(__wake_up_sync_key); /* * __wake_up_sync - see __wake_up_sync_key() */void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive){	__wake_up_sync_key(wq_head, 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). */voidprepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state){	unsigned long flags; 	wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;	spin_lock_irqsave(&wq_head->lock, flags);	if (list_empty(&wq_entry->entry))		__add_wait_queue(wq_head, wq_entry);	set_current_state(state);	spin_unlock_irqrestore(&wq_head->lock, flags);}EXPORT_SYMBOL(prepare_to_wait); voidprepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state){	unsigned long flags; 	wq_entry->flags |= WQ_FLAG_EXCLUSIVE;	spin_lock_irqsave(&wq_head->lock, flags);	if (list_empty(&wq_entry->entry))		__add_wait_queue_entry_tail(wq_head, wq_entry);	set_current_state(state);	spin_unlock_irqrestore(&wq_head->lock, flags);}EXPORT_SYMBOL(prepare_to_wait_exclusive); void init_wait_entry(struct wait_queue_entry *wq_entry, int flags){	wq_entry->flags = flags;	wq_entry->private = current;	wq_entry->func = autoremove_wake_function;	INIT_LIST_HEAD(&wq_entry->entry);}EXPORT_SYMBOL(init_wait_entry); long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state){	unsigned long flags;	long ret = 0; 	spin_lock_irqsave(&wq_head->lock, flags);	if (unlikely(signal_pending_state(state, current))) {		/*		 * Exclusive waiter must not fail if it was selected by wakeup,		 * it should "consume" the condition we were waiting for.		 *		 * The caller will recheck the condition and return success if		 * we were already woken up, we can not miss the event because		 * wakeup locks/unlocks the same wq_head->lock.		 *		 * But we need to ensure that set-condition + wakeup after that		 * can't see us, it should wake up another exclusive waiter if		 * we fail.		 */		list_del_init(&wq_entry->entry);		ret = -ERESTARTSYS;	} else {		if (list_empty(&wq_entry->entry)) {			if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)				__add_wait_queue_entry_tail(wq_head, wq_entry);			else				__add_wait_queue(wq_head, wq_entry);		}		set_current_state(state);	}	spin_unlock_irqrestore(&wq_head->lock, flags); 	return ret;}EXPORT_SYMBOL(prepare_to_wait_event); /* * Note! These two wait functions are entered with the * wait-queue lock held (and interrupts off in the _irq * case), so there is no race with testing the wakeup * condition in the caller before they add the wait * entry to the wake queue. */int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait){	if (likely(list_empty(&wait->entry)))		__add_wait_queue_entry_tail(wq, wait); 	set_current_state(TASK_INTERRUPTIBLE);	if (signal_pending(current))		return -ERESTARTSYS; 	spin_unlock(&wq->lock);	schedule();	spin_lock(&wq->lock);	return 0;}EXPORT_SYMBOL(do_wait_intr); int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait){	if (likely(list_empty(&wait->entry)))		__add_wait_queue_entry_tail(wq, wait); 	set_current_state(TASK_INTERRUPTIBLE);	if (signal_pending(current))		return -ERESTARTSYS; 	spin_unlock_irq(&wq->lock);	schedule();	spin_lock_irq(&wq->lock);	return 0;}EXPORT_SYMBOL(do_wait_intr_irq); /** * finish_wait - clean up after waiting in a queue * @wq_head: waitqueue waited on * @wq_entry: wait descriptor * * Sets current thread back to running state and removes * the wait descriptor from the given waitqueue if still * queued. */void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry){	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(&wq_entry->entry)) {		spin_lock_irqsave(&wq_head->lock, flags);		list_del_init(&wq_entry->entry);		spin_unlock_irqrestore(&wq_head->lock, flags);	}}EXPORT_SYMBOL(finish_wait); int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key){	int ret = default_wake_function(wq_entry, mode, sync, key); 	if (ret)		list_del_init(&wq_entry->entry);	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_head, &wait); * for (;;) { *     if (condition) *         break; * *     p->state = mode;				condition = true; *     smp_mb(); // A				smp_wmb(); // C *     if (!wq_entry->flags & WQ_FLAG_WOKEN)	wq_entry->flags |= WQ_FLAG_WOKEN; *         schedule()				try_to_wake_up(); *     p->state = TASK_RUNNING;		    ~~~~~~~~~~~~~~~~~~ *     wq_entry->flags &= ~WQ_FLAG_WOKEN;		condition = true; *     smp_mb() // B				smp_wmb(); // C *						wq_entry->flags |= WQ_FLAG_WOKEN; * } * remove_wait_queue(&wq_head, &wait); * */long wait_woken(struct wait_queue_entry *wq_entry, 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 (!(wq_entry->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.	 */	smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */ 	return timeout;}EXPORT_SYMBOL(wait_woken); int woken_wake_function(struct wait_queue_entry *wq_entry, 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 smp_store_mb() in wait_woken().	 */	smp_wmb(); /* C */	wq_entry->flags |= WQ_FLAG_WOKEN; 	return default_wake_function(wq_entry, mode, sync, key);}EXPORT_SYMBOL(woken_wake_function);