diff options
Diffstat (limited to 'kernel/sched/wait.c')
| -rw-r--r-- | kernel/sched/wait.c | 486 |
1 files changed, 486 insertions, 0 deletions
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c new file mode 100644 index 000000000..133b74730 --- /dev/null +++ b/kernel/sched/wait.c @@ -0,0 +1,486 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Generic waiting primitives. + * + * (C) 2004 Nadia Yvette Chambers, Oracle + */ + +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(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 add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) +{ + unsigned long flags; + + wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY; + spin_lock_irqsave(&wq_head->lock, flags); + __add_wait_queue(wq_head, wq_entry); + spin_unlock_irqrestore(&wq_head->lock, flags); +} +EXPORT_SYMBOL_GPL(add_wait_queue_priority); + +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); + +/* + * Scan threshold to break wait queue walk. + * This allows a waker to take a break from holding the + * wait queue lock during the wait queue walk. + */ +#define WAITQUEUE_WALK_BREAK_CNT 64 + +/* + * 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 that number of exclusive tasks, and potentially all + * the non-exclusive tasks. Normally, exclusive tasks will be at the end of + * the list and any non-exclusive tasks will be woken first. A priority task + * may be at the head of the list, and can consume the event without any other + * tasks being woken. + * + * 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 int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode, + int nr_exclusive, int wake_flags, void *key, + wait_queue_entry_t *bookmark) +{ + wait_queue_entry_t *curr, *next; + int cnt = 0; + + lockdep_assert_held(&wq_head->lock); + + if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) { + curr = list_next_entry(bookmark, entry); + + list_del(&bookmark->entry); + bookmark->flags = 0; + } else + curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry); + + if (&curr->entry == &wq_head->head) + return nr_exclusive; + + list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) { + unsigned flags = curr->flags; + int ret; + + if (flags & WQ_FLAG_BOOKMARK) + continue; + + ret = curr->func(curr, mode, wake_flags, key); + if (ret < 0) + break; + if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) + break; + + if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) && + (&next->entry != &wq_head->head)) { + bookmark->flags = WQ_FLAG_BOOKMARK; + list_add_tail(&bookmark->entry, &next->entry); + break; + } + } + + return nr_exclusive; +} + +static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode, + int nr_exclusive, int wake_flags, void *key) +{ + unsigned long flags; + wait_queue_entry_t bookmark; + int remaining = nr_exclusive; + + bookmark.flags = 0; + bookmark.private = NULL; + bookmark.func = NULL; + INIT_LIST_HEAD(&bookmark.entry); + + do { + spin_lock_irqsave(&wq_head->lock, flags); + remaining = __wake_up_common(wq_head, mode, remaining, + wake_flags, key, &bookmark); + spin_unlock_irqrestore(&wq_head->lock, flags); + } while (bookmark.flags & WQ_FLAG_BOOKMARK); + + return nr_exclusive - remaining; +} + +/** + * __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 + * + * If this function wakes up a task, it executes a full memory barrier + * before accessing the task state. Returns the number of exclusive + * tasks that were awaken. + */ +int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, + int nr_exclusive, void *key) +{ + return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key); +} +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, 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, NULL); +} +EXPORT_SYMBOL_GPL(__wake_up_locked_key); + +void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head, + unsigned int mode, void *key, wait_queue_entry_t *bookmark) +{ + __wake_up_common(wq_head, mode, 1, 0, key, bookmark); +} +EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark); + +/** + * __wake_up_sync_key - wake up threads blocked on a waitqueue. + * @wq_head: the waitqueue + * @mode: which threads + * @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. + * + * If this function wakes up a task, it executes a full memory barrier before + * accessing the task state. + */ +void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, + void *key) +{ + if (unlikely(!wq_head)) + return; + + __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key); +} +EXPORT_SYMBOL_GPL(__wake_up_sync_key); + +/** + * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue. + * @wq_head: the waitqueue + * @mode: which threads + * @key: opaque value to be passed to wakeup targets + * + * The sync wakeup differs in 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. + * + * If this function wakes up a task, it executes a full memory barrier before + * accessing the task state. + */ +void __wake_up_locked_sync_key(struct wait_queue_head *wq_head, + unsigned int mode, void *key) +{ + __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL); +} +EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key); + +/* + * __wake_up_sync - see __wake_up_sync_key() + */ +void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode) +{ + __wake_up_sync_key(wq_head, mode, NULL); +} +EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */ + +void __wake_up_pollfree(struct wait_queue_head *wq_head) +{ + __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE)); + /* POLLFREE must have cleared the queue. */ + WARN_ON_ONCE(waitqueue_active(wq_head)); +} + +/* + * 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(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); + +/* Returns true if we are the first waiter in the queue, false otherwise. */ +bool +prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state) +{ + unsigned long flags; + bool was_empty = false; + + wq_entry->flags |= WQ_FLAG_EXCLUSIVE; + spin_lock_irqsave(&wq_head->lock, flags); + if (list_empty(&wq_entry->entry)) { + was_empty = list_empty(&wq_head->head); + __add_wait_queue_entry_tail(wq_head, wq_entry); + } + set_current_state(state); + spin_unlock_irqrestore(&wq_head->lock, flags); + return was_empty; +} +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 (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_careful(&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; + * + * // in wait_woken() // in woken_wake_function() + * + * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN; + * smp_mb(); // A try_to_wake_up(): + * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier> + * schedule() if (p->state & mode) + * p->state = TASK_RUNNING; p->state = TASK_RUNNING; + * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~ + * smp_mb(); // B condition = true; + * } smp_mb(); // C + * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN; + */ +long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout) +{ + /* + * The below executes an smp_mb(), which matches with the full barrier + * executed by the try_to_wake_up() in woken_wake_function() such that + * either we see the store to wq_entry->flags in woken_wake_function() + * or woken_wake_function() sees our store to current->state. + */ + set_current_state(mode); /* A */ + if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop()) + timeout = schedule_timeout(timeout); + __set_current_state(TASK_RUNNING); + + /* + * The below executes an smp_mb(), which matches with the smp_mb() (C) + * in woken_wake_function() such that either we see the wait condition + * being true or the store to wq_entry->flags in woken_wake_function() + * follows ours in the coherence order. + */ + 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) +{ + /* Pairs with the smp_store_mb() in wait_woken(). */ + smp_mb(); /* C */ + wq_entry->flags |= WQ_FLAG_WOKEN; + + return default_wake_function(wq_entry, mode, sync, key); +} +EXPORT_SYMBOL(woken_wake_function); |