/* * 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). */voidprepare_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); voidprepare_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); void init_wait_entry(wait_queue_t *wait, int flags){ wait->flags = flags; wait->private = current; wait->func = autoremove_wake_function; INIT_LIST_HEAD(&wait->task_list);}EXPORT_SYMBOL(init_wait_entry); long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state){ unsigned long flags; long ret = 0; spin_lock_irqsave(&q->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 q->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(&wait->task_list); ret = -ERESTARTSYS; } else { 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 ret;}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); 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. */ smp_store_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 smp_store_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, mode); } 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){ int ret = 0; for (;;) { prepare_to_wait_exclusive(wq, &q->wait, mode); if (test_bit(q->key.bit_nr, q->key.flags)) { ret = action(&q->key, mode); /* * See the comment in prepare_to_wait_event(). * finish_wait() does not necessarily takes wq->lock, * but test_and_set_bit() implies mb() which pairs with * smp_mb__after_atomic() before wake_up_page(). */ if (ret) finish_wait(wq, &q->wait); } if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) { if (!ret) finish_wait(wq, &q->wait); return 0; } else if (ret) { return ret; } }}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); /* * 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;Lines 1–500 of 611. Load more
/* * 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); void init_wait_entry(wait_queue_t *wait, int flags) { wait->flags = flags; wait->private = current; wait->func = autoremove_wake_function; INIT_LIST_HEAD(&wait->task_list); } EXPORT_SYMBOL(init_wait_entry); long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state) { unsigned long flags; long ret = 0; spin_lock_irqsave(&q->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 q->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(&wait->task_list); ret = -ERESTARTSYS; } else { 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 ret; } 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); 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. */ smp_store_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 smp_store_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, mode); } 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) { int ret = 0; for (;;) { prepare_to_wait_exclusive(wq, &q->wait, mode); if (test_bit(q->key.bit_nr, q->key.flags)) { ret = action(&q->key, mode); /* * See the comment in prepare_to_wait_event(). * finish_wait() does not necessarily takes wq->lock, * but test_and_set_bit() implies mb() which pairs with * smp_mb__after_atomic() before wake_up_page(). */ if (ret) finish_wait(wq, &q->wait); } if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) { if (!ret) finish_wait(wq, &q->wait); return 0; } else if (ret) { return ret; } } } 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); /* * 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;