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| author |   Peter Zijlstra <peterz@infradead.org> | 2018-12-17 10:14:53 +0100 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2019-01-21 11:15:36 +0100 |
| commit | e6018c0f5c996e61639adce6a0697391a2861916 (patch) | |
| tree | 280797731862759271bf6f2ec09813ae5527ffc7 /include | |
| parent | sched/wait: Fix rcuwait_wake_up() ordering (diff) | |
| download | linux-dev-e6018c0f5c996e61639adce6a0697391a2861916.tar.xz linux-dev-e6018c0f5c996e61639adce6a0697391a2861916.zip | |
sched/wake_q: Document wake_q_add()
The only guarantee provided by wake_q_add() is that a wakeup will
happen after it, it does _NOT_ guarantee the wakeup will be delayed
until the matching wake_up_q().
If wake_q_add() fails the cmpxchg() a concurrent wakeup is pending and
that can happen at any time after the cmpxchg(). This means we should
not rely on the wakeup happening at wake_q_up(), but should be ready
for wake_q_add() to issue the wakeup.
The delay; if provided (most likely); should only result in more efficient
behaviour.
Reported-by: Yongji Xie <elohimes@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/sched/wake_q.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/sched/wake_q.h b/include/linux/sched/wake_q.h index 10b19a192b2d..545f37138057 100644 --- a/include/linux/sched/wake_q.h +++ b/include/linux/sched/wake_q.h @@ -24,9 +24,13 @@ * called near the end of a function. Otherwise, the list can be * re-initialized for later re-use by wake_q_init(). * - * Note that this can cause spurious wakeups. schedule() callers + * NOTE that this can cause spurious wakeups. schedule() callers * must ensure the call is done inside a loop, confirming that the * wakeup condition has in fact occurred. + * + * NOTE that there is no guarantee the wakeup will happen any later than the + * wake_q_add() location. Therefore task must be ready to be woken at the + * location of the wake_q_add(). */ #include <linux/sched.h> |