linux/kernel/sched/wait.c

// 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)
{ … }

EXPORT_SYMBOL(…);

void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{ … }
EXPORT_SYMBOL(…);

void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{ … }
EXPORT_SYMBOL(…);

void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{ … }
EXPORT_SYMBOL_GPL(…);

void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{ … }
EXPORT_SYMBOL(…);

/*
 * 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)
{ … }

static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
			int nr_exclusive, int wake_flags, void *key)
{ … }

/**
 * __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)
{ … }
EXPORT_SYMBOL(…);

void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key)
{ … }

/*
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * __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)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * __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)
{ … }
EXPORT_SYMBOL_GPL(…);

/*
 * __wake_up_sync - see __wake_up_sync_key()
 */
void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
{ … }
EXPORT_SYMBOL_GPL(…);	/* For internal use only */

void __wake_up_pollfree(struct wait_queue_head *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)
{ … }
EXPORT_SYMBOL(…);

/* 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)
{ … }
EXPORT_SYMBOL(…);

void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
{ … }
EXPORT_SYMBOL(…);

long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
{ … }
EXPORT_SYMBOL(…);

/*
 * 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)
{ … }
EXPORT_SYMBOL(…);

int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
{ … }
EXPORT_SYMBOL(…);

/*
 * 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)
{ … }
EXPORT_SYMBOL(…);

int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
{ … }
EXPORT_SYMBOL(…);