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![Linus Torvalds](/assets/img/avatar_default.png)
The scheduler header file split and cleanups ended up exposing a few
nasty header file dependencies, and in particular it showed how we in
<linux/wait.h> ended up depending on "signal_pending()", which now comes
from <linux/sched/signal.h>.
That's a very subtle and annoying dependency, which already caused a
semantic merge conflict (see commit e58bc92783
"Pull overlayfs updates
from Miklos Szeredi", which added that fixup in the merge commit).
It turns out that we can avoid this dependency _and_ improve code
generation by moving the guts of the fairly nasty helper #define
__wait_event_interruptible_locked() to out-of-line code. The code that
includes the signal_pending() check is all in the slow-path where we
actually go to sleep waiting for the event anyway, so using a helper
function is the right thing to do.
Using a helper function is also what we already did for the non-locked
versions, see the "__wait_event*()" macros and the "prepare_to_wait*()"
set of helper functions.
We might want to try to unify all these macro games, we have a _lot_ of
subtly different wait-event loops. But this is the minimal patch to fix
the annoying header dependency.
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
651 lines
18 KiB
C
651 lines
18 KiB
C
/*
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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 <linux/init.h>
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#include <linux/export.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/debug.h>
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#include <linux/mm.h>
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#include <linux/wait.h>
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#include <linux/hash.h>
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#include <linux/kthread.h>
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void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
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{
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spin_lock_init(&q->lock);
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lockdep_set_class_and_name(&q->lock, key, name);
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INIT_LIST_HEAD(&q->task_list);
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}
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EXPORT_SYMBOL(__init_waitqueue_head);
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void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
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{
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unsigned long flags;
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wait->flags &= ~WQ_FLAG_EXCLUSIVE;
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spin_lock_irqsave(&q->lock, flags);
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__add_wait_queue(q, wait);
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spin_unlock_irqrestore(&q->lock, flags);
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}
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EXPORT_SYMBOL(add_wait_queue);
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void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
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{
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unsigned long flags;
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wait->flags |= WQ_FLAG_EXCLUSIVE;
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spin_lock_irqsave(&q->lock, flags);
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__add_wait_queue_tail(q, wait);
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spin_unlock_irqrestore(&q->lock, flags);
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}
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EXPORT_SYMBOL(add_wait_queue_exclusive);
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void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
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{
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unsigned long flags;
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spin_lock_irqsave(&q->lock, flags);
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__remove_wait_queue(q, wait);
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spin_unlock_irqrestore(&q->lock, flags);
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}
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EXPORT_SYMBOL(remove_wait_queue);
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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 all the non-exclusive tasks and one exclusive task.
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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 void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
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int nr_exclusive, int wake_flags, void *key)
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{
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wait_queue_t *curr, *next;
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list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
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unsigned flags = curr->flags;
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if (curr->func(curr, mode, wake_flags, key) &&
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(flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
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break;
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}
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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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* @q: 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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* It may be assumed that this function implies a write memory barrier before
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* changing the task state if and only if any tasks are woken up.
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*/
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void __wake_up(wait_queue_head_t *q, unsigned int mode,
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int nr_exclusive, void *key)
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{
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unsigned long flags;
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spin_lock_irqsave(&q->lock, flags);
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__wake_up_common(q, mode, nr_exclusive, 0, key);
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spin_unlock_irqrestore(&q->lock, flags);
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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(wait_queue_head_t *q, unsigned int mode, int nr)
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{
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__wake_up_common(q, mode, nr, 0, NULL);
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}
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EXPORT_SYMBOL_GPL(__wake_up_locked);
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void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
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{
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__wake_up_common(q, mode, 1, 0, key);
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}
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EXPORT_SYMBOL_GPL(__wake_up_locked_key);
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/**
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* __wake_up_sync_key - wake up threads blocked on a waitqueue.
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* @q: 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: 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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* It may be assumed that this function implies a write memory barrier before
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* changing the task state if and only if any tasks are woken up.
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*/
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void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
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int nr_exclusive, void *key)
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{
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unsigned long flags;
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int wake_flags = 1; /* XXX WF_SYNC */
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if (unlikely(!q))
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return;
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if (unlikely(nr_exclusive != 1))
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wake_flags = 0;
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spin_lock_irqsave(&q->lock, flags);
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__wake_up_common(q, mode, nr_exclusive, wake_flags, key);
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spin_unlock_irqrestore(&q->lock, flags);
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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_sync - see __wake_up_sync_key()
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*/
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void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
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{
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__wake_up_sync_key(q, mode, nr_exclusive, 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(wait_queue_head_t *q, wait_queue_t *wait, int state)
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{
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unsigned long flags;
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wait->flags &= ~WQ_FLAG_EXCLUSIVE;
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spin_lock_irqsave(&q->lock, flags);
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if (list_empty(&wait->task_list))
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__add_wait_queue(q, wait);
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set_current_state(state);
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spin_unlock_irqrestore(&q->lock, flags);
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}
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EXPORT_SYMBOL(prepare_to_wait);
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void
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prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
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{
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unsigned long flags;
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wait->flags |= WQ_FLAG_EXCLUSIVE;
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spin_lock_irqsave(&q->lock, flags);
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if (list_empty(&wait->task_list))
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__add_wait_queue_tail(q, wait);
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set_current_state(state);
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spin_unlock_irqrestore(&q->lock, flags);
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}
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EXPORT_SYMBOL(prepare_to_wait_exclusive);
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void init_wait_entry(wait_queue_t *wait, int flags)
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{
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wait->flags = flags;
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wait->private = current;
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wait->func = autoremove_wake_function;
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INIT_LIST_HEAD(&wait->task_list);
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}
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EXPORT_SYMBOL(init_wait_entry);
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long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, 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(&q->lock, flags);
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if (unlikely(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 q->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(&wait->task_list);
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ret = -ERESTARTSYS;
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} else {
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if (list_empty(&wait->task_list)) {
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if (wait->flags & WQ_FLAG_EXCLUSIVE)
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__add_wait_queue_tail(q, wait);
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else
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__add_wait_queue(q, wait);
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}
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set_current_state(state);
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}
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spin_unlock_irqrestore(&q->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_t *wait)
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{
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if (likely(list_empty(&wait->task_list)))
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__add_wait_queue_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_t *wait)
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{
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if (likely(list_empty(&wait->task_list)))
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__add_wait_queue_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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* @q: waitqueue waited on
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* @wait: 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(wait_queue_head_t *q, wait_queue_t *wait)
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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(&wait->task_list)) {
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spin_lock_irqsave(&q->lock, flags);
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list_del_init(&wait->task_list);
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spin_unlock_irqrestore(&q->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(wait_queue_t *wait, unsigned mode, int sync, void *key)
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{
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int ret = default_wake_function(wait, mode, sync, key);
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if (ret)
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list_del_init(&wait->task_list);
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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, &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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* p->state = mode; condition = true;
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* smp_mb(); // A smp_wmb(); // C
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* if (!wait->flags & WQ_FLAG_WOKEN) wait->flags |= WQ_FLAG_WOKEN;
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* schedule() try_to_wake_up();
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* p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
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* wait->flags &= ~WQ_FLAG_WOKEN; condition = true;
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* smp_mb() // B smp_wmb(); // C
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* wait->flags |= WQ_FLAG_WOKEN;
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* }
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* remove_wait_queue(&wq, &wait);
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*
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*/
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long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
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{
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set_current_state(mode); /* A */
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/*
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* The above implies an smp_mb(), which matches with the smp_wmb() from
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* woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
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* also observe all state before the wakeup.
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*/
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if (!(wait->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 implies an smp_mb(), it too pairs with the smp_wmb() from
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* woken_wake_function() such that we must either observe the wait
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* condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
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* an event.
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*/
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smp_store_mb(wait->flags, wait->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(wait_queue_t *wait, unsigned mode, int sync, void *key)
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{
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/*
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* Although this function is called under waitqueue lock, LOCK
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* doesn't imply write barrier and the users expects write
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* barrier semantics on wakeup functions. The following
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* smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
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* and is paired with smp_store_mb() in wait_woken().
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*/
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smp_wmb(); /* C */
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wait->flags |= WQ_FLAG_WOKEN;
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return default_wake_function(wait, mode, sync, key);
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}
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EXPORT_SYMBOL(woken_wake_function);
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int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
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{
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struct wait_bit_key *key = arg;
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struct wait_bit_queue *wait_bit
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= container_of(wait, struct wait_bit_queue, wait);
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if (wait_bit->key.flags != key->flags ||
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wait_bit->key.bit_nr != key->bit_nr ||
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test_bit(key->bit_nr, key->flags))
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return 0;
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else
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return autoremove_wake_function(wait, mode, sync, key);
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}
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EXPORT_SYMBOL(wake_bit_function);
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/*
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* To allow interruptible waiting and asynchronous (i.e. nonblocking)
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* waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
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* permitted return codes. Nonzero return codes halt waiting and return.
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*/
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int __sched
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__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
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wait_bit_action_f *action, unsigned mode)
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{
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int ret = 0;
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do {
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prepare_to_wait(wq, &q->wait, mode);
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if (test_bit(q->key.bit_nr, q->key.flags))
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ret = (*action)(&q->key, mode);
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} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
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finish_wait(wq, &q->wait);
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return ret;
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}
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EXPORT_SYMBOL(__wait_on_bit);
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int __sched out_of_line_wait_on_bit(void *word, int bit,
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wait_bit_action_f *action, unsigned mode)
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{
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wait_queue_head_t *wq = bit_waitqueue(word, bit);
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DEFINE_WAIT_BIT(wait, word, bit);
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return __wait_on_bit(wq, &wait, action, mode);
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}
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EXPORT_SYMBOL(out_of_line_wait_on_bit);
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int __sched out_of_line_wait_on_bit_timeout(
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void *word, int bit, wait_bit_action_f *action,
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unsigned mode, unsigned long timeout)
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{
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wait_queue_head_t *wq = bit_waitqueue(word, bit);
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DEFINE_WAIT_BIT(wait, word, bit);
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wait.key.timeout = jiffies + timeout;
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return __wait_on_bit(wq, &wait, action, mode);
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}
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EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
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int __sched
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__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
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wait_bit_action_f *action, unsigned mode)
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{
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int ret = 0;
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for (;;) {
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prepare_to_wait_exclusive(wq, &q->wait, mode);
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if (test_bit(q->key.bit_nr, q->key.flags)) {
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ret = action(&q->key, mode);
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/*
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* 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;
|
|
struct wait_bit_queue *wait_bit
|
|
= container_of(wait, struct wait_bit_queue, wait);
|
|
atomic_t *val = key->flags;
|
|
|
|
if (wait_bit->key.flags != key->flags ||
|
|
wait_bit->key.bit_nr != key->bit_nr ||
|
|
atomic_read(val) != 0)
|
|
return 0;
|
|
return autoremove_wake_function(wait, mode, sync, key);
|
|
}
|
|
|
|
/*
|
|
* To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
|
|
* the actions of __wait_on_atomic_t() are permitted return codes. Nonzero
|
|
* return codes halt waiting and return.
|
|
*/
|
|
static __sched
|
|
int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
|
|
int (*action)(atomic_t *), unsigned mode)
|
|
{
|
|
atomic_t *val;
|
|
int ret = 0;
|
|
|
|
do {
|
|
prepare_to_wait(wq, &q->wait, mode);
|
|
val = q->key.flags;
|
|
if (atomic_read(val) == 0)
|
|
break;
|
|
ret = (*action)(val);
|
|
} while (!ret && atomic_read(val) != 0);
|
|
finish_wait(wq, &q->wait);
|
|
return ret;
|
|
}
|
|
|
|
#define DEFINE_WAIT_ATOMIC_T(name, p) \
|
|
struct wait_bit_queue name = { \
|
|
.key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p), \
|
|
.wait = { \
|
|
.private = current, \
|
|
.func = wake_atomic_t_function, \
|
|
.task_list = \
|
|
LIST_HEAD_INIT((name).wait.task_list), \
|
|
}, \
|
|
}
|
|
|
|
__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
|
|
unsigned mode)
|
|
{
|
|
wait_queue_head_t *wq = atomic_t_waitqueue(p);
|
|
DEFINE_WAIT_ATOMIC_T(wait, p);
|
|
|
|
return __wait_on_atomic_t(wq, &wait, action, mode);
|
|
}
|
|
EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
|
|
|
|
/**
|
|
* wake_up_atomic_t - Wake up a waiter on a atomic_t
|
|
* @p: The atomic_t being waited on, a kernel virtual address
|
|
*
|
|
* Wake up anyone waiting for the atomic_t to go to zero.
|
|
*
|
|
* Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
|
|
* check is done by the waiter's wake function, not the by the waker itself).
|
|
*/
|
|
void wake_up_atomic_t(atomic_t *p)
|
|
{
|
|
__wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
|
|
}
|
|
EXPORT_SYMBOL(wake_up_atomic_t);
|
|
|
|
__sched int bit_wait(struct wait_bit_key *word, int mode)
|
|
{
|
|
schedule();
|
|
if (signal_pending_state(mode, current))
|
|
return -EINTR;
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL(bit_wait);
|
|
|
|
__sched int bit_wait_io(struct wait_bit_key *word, int mode)
|
|
{
|
|
io_schedule();
|
|
if (signal_pending_state(mode, current))
|
|
return -EINTR;
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL(bit_wait_io);
|
|
|
|
__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
|
|
{
|
|
unsigned long now = READ_ONCE(jiffies);
|
|
if (time_after_eq(now, word->timeout))
|
|
return -EAGAIN;
|
|
schedule_timeout(word->timeout - now);
|
|
if (signal_pending_state(mode, current))
|
|
return -EINTR;
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL_GPL(bit_wait_timeout);
|
|
|
|
__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
|
|
{
|
|
unsigned long now = READ_ONCE(jiffies);
|
|
if (time_after_eq(now, word->timeout))
|
|
return -EAGAIN;
|
|
io_schedule_timeout(word->timeout - now);
|
|
if (signal_pending_state(mode, current))
|
|
return -EINTR;
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
|