sched/wake_q: Document wake_q_add()
authorPeter Zijlstra <peterz@infradead.org>
Mon, 17 Dec 2018 09:14:53 +0000 (10:14 +0100)
committerIngo Molnar <mingo@kernel.org>
Mon, 21 Jan 2019 10:15:36 +0000 (11:15 +0100)
commite6018c0f5c996e61639adce6a0697391a2861916
tree280797731862759271bf6f2ec09813ae5527ffc7
parent6dc080eeb2ba01973bfff0d79844d7a59e12542e
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>
include/linux/sched/wake_q.h
kernel/sched/core.c