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476 lines
14 KiB
476 lines
14 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Generic waiting primitives. |
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* |
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* (C) 2004 Nadia Yvette Chambers, Oracle |
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*/ |
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#include "sched.h" |
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void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key) |
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{ |
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spin_lock_init(&wq_head->lock); |
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lockdep_set_class_and_name(&wq_head->lock, key, name); |
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INIT_LIST_HEAD(&wq_head->head); |
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} |
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EXPORT_SYMBOL(__init_waitqueue_head); |
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void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
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{ |
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unsigned long flags; |
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wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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__add_wait_queue(wq_head, wq_entry); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} |
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EXPORT_SYMBOL(add_wait_queue); |
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void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
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{ |
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unsigned long flags; |
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wq_entry->flags |= WQ_FLAG_EXCLUSIVE; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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__add_wait_queue_entry_tail(wq_head, wq_entry); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} |
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EXPORT_SYMBOL(add_wait_queue_exclusive); |
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void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
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{ |
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unsigned long flags; |
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wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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__add_wait_queue(wq_head, wq_entry); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} |
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EXPORT_SYMBOL_GPL(add_wait_queue_priority); |
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void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
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{ |
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unsigned long flags; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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__remove_wait_queue(wq_head, wq_entry); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} |
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EXPORT_SYMBOL(remove_wait_queue); |
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/* |
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* Scan threshold to break wait queue walk. |
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* This allows a waker to take a break from holding the |
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* wait queue lock during the wait queue walk. |
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*/ |
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#define WAITQUEUE_WALK_BREAK_CNT 64 |
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/* |
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* The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just |
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* wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve |
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* number) then we wake that number of exclusive tasks, and potentially all |
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* the non-exclusive tasks. Normally, exclusive tasks will be at the end of |
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* the list and any non-exclusive tasks will be woken first. A priority task |
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* may be at the head of the list, and can consume the event without any other |
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* tasks being woken. |
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* |
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* There are circumstances in which we can try to wake a task which has already |
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* started to run but is not in state TASK_RUNNING. try_to_wake_up() returns |
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* zero in this (rare) case, and we handle it by continuing to scan the queue. |
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*/ |
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static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, |
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int nr_exclusive, int wake_flags, void *key, |
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wait_queue_entry_t *bookmark) |
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{ |
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wait_queue_entry_t *curr, *next; |
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int cnt = 0; |
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lockdep_assert_held(&wq_head->lock); |
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if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) { |
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curr = list_next_entry(bookmark, entry); |
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list_del(&bookmark->entry); |
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bookmark->flags = 0; |
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} else |
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curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry); |
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if (&curr->entry == &wq_head->head) |
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return nr_exclusive; |
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list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) { |
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unsigned flags = curr->flags; |
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int ret; |
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if (flags & WQ_FLAG_BOOKMARK) |
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continue; |
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ret = curr->func(curr, mode, wake_flags, key); |
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if (ret < 0) |
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break; |
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if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) |
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break; |
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if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) && |
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(&next->entry != &wq_head->head)) { |
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bookmark->flags = WQ_FLAG_BOOKMARK; |
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list_add_tail(&bookmark->entry, &next->entry); |
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break; |
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} |
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} |
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return nr_exclusive; |
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} |
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static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode, |
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int nr_exclusive, int wake_flags, void *key) |
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{ |
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unsigned long flags; |
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wait_queue_entry_t bookmark; |
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bookmark.flags = 0; |
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bookmark.private = NULL; |
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bookmark.func = NULL; |
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INIT_LIST_HEAD(&bookmark.entry); |
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do { |
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spin_lock_irqsave(&wq_head->lock, flags); |
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nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, |
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wake_flags, key, &bookmark); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} while (bookmark.flags & WQ_FLAG_BOOKMARK); |
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} |
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/** |
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* __wake_up - wake up threads blocked on a waitqueue. |
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* @wq_head: the waitqueue |
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* @mode: which threads |
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* @nr_exclusive: how many wake-one or wake-many threads to wake up |
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* @key: is directly passed to the wakeup function |
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* |
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* If this function wakes up a task, it executes a full memory barrier before |
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* accessing the task state. |
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*/ |
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void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, |
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int nr_exclusive, void *key) |
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{ |
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__wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key); |
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} |
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EXPORT_SYMBOL(__wake_up); |
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/* |
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* Same as __wake_up but called with the spinlock in wait_queue_head_t held. |
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*/ |
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void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr) |
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{ |
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__wake_up_common(wq_head, mode, nr, 0, NULL, NULL); |
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} |
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EXPORT_SYMBOL_GPL(__wake_up_locked); |
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void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key) |
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{ |
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__wake_up_common(wq_head, mode, 1, 0, key, NULL); |
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} |
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EXPORT_SYMBOL_GPL(__wake_up_locked_key); |
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void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head, |
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unsigned int mode, void *key, wait_queue_entry_t *bookmark) |
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{ |
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__wake_up_common(wq_head, mode, 1, 0, key, bookmark); |
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} |
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EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark); |
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/** |
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* __wake_up_sync_key - wake up threads blocked on a waitqueue. |
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* @wq_head: the waitqueue |
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* @mode: which threads |
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* @key: opaque value to be passed to wakeup targets |
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* |
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* The sync wakeup differs that the waker knows that it will schedule |
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* away soon, so while the target thread will be woken up, it will not |
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* be migrated to another CPU - ie. the two threads are 'synchronized' |
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* with each other. This can prevent needless bouncing between CPUs. |
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* |
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* On UP it can prevent extra preemption. |
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* |
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* If this function wakes up a task, it executes a full memory barrier before |
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* accessing the task state. |
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*/ |
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void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, |
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void *key) |
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{ |
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if (unlikely(!wq_head)) |
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return; |
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__wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key); |
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} |
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EXPORT_SYMBOL_GPL(__wake_up_sync_key); |
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/** |
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* __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue. |
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* @wq_head: the waitqueue |
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* @mode: which threads |
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* @key: opaque value to be passed to wakeup targets |
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* |
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* The sync wakeup differs in that the waker knows that it will schedule |
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* away soon, so while the target thread will be woken up, it will not |
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* be migrated to another CPU - ie. the two threads are 'synchronized' |
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* with each other. This can prevent needless bouncing between CPUs. |
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* |
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* On UP it can prevent extra preemption. |
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* |
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* If this function wakes up a task, it executes a full memory barrier before |
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* accessing the task state. |
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*/ |
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void __wake_up_locked_sync_key(struct wait_queue_head *wq_head, |
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unsigned int mode, void *key) |
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{ |
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__wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL); |
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} |
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EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key); |
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/* |
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* __wake_up_sync - see __wake_up_sync_key() |
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*/ |
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void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode) |
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{ |
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__wake_up_sync_key(wq_head, mode, NULL); |
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} |
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EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */ |
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/* |
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* Note: we use "set_current_state()" _after_ the wait-queue add, |
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* because we need a memory barrier there on SMP, so that any |
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* wake-function that tests for the wait-queue being active |
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* will be guaranteed to see waitqueue addition _or_ subsequent |
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* tests in this thread will see the wakeup having taken place. |
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* |
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* The spin_unlock() itself is semi-permeable and only protects |
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* one way (it only protects stuff inside the critical region and |
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* stops them from bleeding out - it would still allow subsequent |
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* loads to move into the critical region). |
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*/ |
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void |
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prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
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{ |
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unsigned long flags; |
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wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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if (list_empty(&wq_entry->entry)) |
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__add_wait_queue(wq_head, wq_entry); |
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set_current_state(state); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} |
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EXPORT_SYMBOL(prepare_to_wait); |
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/* Returns true if we are the first waiter in the queue, false otherwise. */ |
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bool |
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prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
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{ |
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unsigned long flags; |
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bool was_empty = false; |
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wq_entry->flags |= WQ_FLAG_EXCLUSIVE; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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if (list_empty(&wq_entry->entry)) { |
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was_empty = list_empty(&wq_head->head); |
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__add_wait_queue_entry_tail(wq_head, wq_entry); |
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} |
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set_current_state(state); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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return was_empty; |
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} |
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EXPORT_SYMBOL(prepare_to_wait_exclusive); |
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void init_wait_entry(struct wait_queue_entry *wq_entry, int flags) |
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{ |
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wq_entry->flags = flags; |
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wq_entry->private = current; |
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wq_entry->func = autoremove_wake_function; |
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INIT_LIST_HEAD(&wq_entry->entry); |
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} |
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EXPORT_SYMBOL(init_wait_entry); |
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long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) |
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{ |
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unsigned long flags; |
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long ret = 0; |
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spin_lock_irqsave(&wq_head->lock, flags); |
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if (signal_pending_state(state, current)) { |
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/* |
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* Exclusive waiter must not fail if it was selected by wakeup, |
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* it should "consume" the condition we were waiting for. |
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* |
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* The caller will recheck the condition and return success if |
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* we were already woken up, we can not miss the event because |
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* wakeup locks/unlocks the same wq_head->lock. |
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* |
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* But we need to ensure that set-condition + wakeup after that |
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* can't see us, it should wake up another exclusive waiter if |
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* we fail. |
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*/ |
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list_del_init(&wq_entry->entry); |
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ret = -ERESTARTSYS; |
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} else { |
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if (list_empty(&wq_entry->entry)) { |
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if (wq_entry->flags & WQ_FLAG_EXCLUSIVE) |
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__add_wait_queue_entry_tail(wq_head, wq_entry); |
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else |
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__add_wait_queue(wq_head, wq_entry); |
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} |
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set_current_state(state); |
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} |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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return ret; |
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} |
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EXPORT_SYMBOL(prepare_to_wait_event); |
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/* |
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* Note! These two wait functions are entered with the |
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* wait-queue lock held (and interrupts off in the _irq |
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* case), so there is no race with testing the wakeup |
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* condition in the caller before they add the wait |
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* entry to the wake queue. |
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*/ |
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int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait) |
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{ |
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if (likely(list_empty(&wait->entry))) |
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__add_wait_queue_entry_tail(wq, wait); |
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set_current_state(TASK_INTERRUPTIBLE); |
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if (signal_pending(current)) |
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return -ERESTARTSYS; |
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spin_unlock(&wq->lock); |
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schedule(); |
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spin_lock(&wq->lock); |
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return 0; |
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} |
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EXPORT_SYMBOL(do_wait_intr); |
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int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait) |
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{ |
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if (likely(list_empty(&wait->entry))) |
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__add_wait_queue_entry_tail(wq, wait); |
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set_current_state(TASK_INTERRUPTIBLE); |
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if (signal_pending(current)) |
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return -ERESTARTSYS; |
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spin_unlock_irq(&wq->lock); |
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schedule(); |
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spin_lock_irq(&wq->lock); |
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return 0; |
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} |
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EXPORT_SYMBOL(do_wait_intr_irq); |
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/** |
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* finish_wait - clean up after waiting in a queue |
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* @wq_head: waitqueue waited on |
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* @wq_entry: wait descriptor |
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* |
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* Sets current thread back to running state and removes |
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* the wait descriptor from the given waitqueue if still |
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* queued. |
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*/ |
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void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) |
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{ |
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unsigned long flags; |
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__set_current_state(TASK_RUNNING); |
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/* |
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* We can check for list emptiness outside the lock |
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* IFF: |
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* - we use the "careful" check that verifies both |
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* the next and prev pointers, so that there cannot |
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* be any half-pending updates in progress on other |
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* CPU's that we haven't seen yet (and that might |
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* still change the stack area. |
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* and |
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* - all other users take the lock (ie we can only |
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* have _one_ other CPU that looks at or modifies |
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* the list). |
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*/ |
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if (!list_empty_careful(&wq_entry->entry)) { |
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spin_lock_irqsave(&wq_head->lock, flags); |
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list_del_init(&wq_entry->entry); |
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spin_unlock_irqrestore(&wq_head->lock, flags); |
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} |
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} |
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EXPORT_SYMBOL(finish_wait); |
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int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) |
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{ |
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int ret = default_wake_function(wq_entry, mode, sync, key); |
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if (ret) |
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list_del_init_careful(&wq_entry->entry); |
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return ret; |
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} |
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EXPORT_SYMBOL(autoremove_wake_function); |
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static inline bool is_kthread_should_stop(void) |
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{ |
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return (current->flags & PF_KTHREAD) && kthread_should_stop(); |
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} |
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/* |
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* DEFINE_WAIT_FUNC(wait, woken_wake_func); |
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* |
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* add_wait_queue(&wq_head, &wait); |
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* for (;;) { |
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* if (condition) |
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* break; |
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* |
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* // in wait_woken() // in woken_wake_function() |
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* |
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* p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN; |
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* smp_mb(); // A try_to_wake_up(): |
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* if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier> |
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* schedule() if (p->state & mode) |
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* p->state = TASK_RUNNING; p->state = TASK_RUNNING; |
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* wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~ |
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* smp_mb(); // B condition = true; |
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* } smp_mb(); // C |
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* remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN; |
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*/ |
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long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) |
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{ |
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/* |
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* The below executes an smp_mb(), which matches with the full barrier |
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* executed by the try_to_wake_up() in woken_wake_function() such that |
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* either we see the store to wq_entry->flags in woken_wake_function() |
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* or woken_wake_function() sees our store to current->state. |
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*/ |
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set_current_state(mode); /* A */ |
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if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop()) |
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timeout = schedule_timeout(timeout); |
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__set_current_state(TASK_RUNNING); |
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/* |
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* The below executes an smp_mb(), which matches with the smp_mb() (C) |
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* in woken_wake_function() such that either we see the wait condition |
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* being true or the store to wq_entry->flags in woken_wake_function() |
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* follows ours in the coherence order. |
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*/ |
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smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */ |
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return timeout; |
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} |
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EXPORT_SYMBOL(wait_woken); |
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int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key) |
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{ |
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/* Pairs with the smp_store_mb() in wait_woken(). */ |
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smp_mb(); /* C */ |
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wq_entry->flags |= WQ_FLAG_WOKEN; |
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return default_wake_function(wq_entry, mode, sync, key); |
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} |
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EXPORT_SYMBOL(woken_wake_function);
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