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SubjectRe: wait_for_completion_timeout() spurious failure under heavy load?

* Oleg Nesterov <oleg@tv-sign.ru> wrote:

> > IOW, how about the patch below? this also makes the code a bit
> > simpler because we factor out __remove_wait_queue().
>
> Even better, we can kill the first __remove_wait_queue() as well.

nice, thanks - applied it in the form below to tip/sched/urgent.

Ingo

------------------>
commit 6b8464474776dccf619283ee5510b0b795382dfb
Author: Oleg Nesterov <oleg@tv-sign.ru>
Date: Fri Jun 20 18:32:20 2008 +0400

sched: refactor wait_for_completion_timeout()

Simplify the code and fix the boundary condition of
wait_for_completion_timeout(,0).

We can kill the first __remove_wait_queue() as well.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 577f160..bebf978 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4398,32 +4398,20 @@ do_wait_for_common(struct completion *x, long timeout, int state)
signal_pending(current)) ||
(state == TASK_KILLABLE &&
fatal_signal_pending(current))) {
- __remove_wait_queue(&x->wait, &wait);
- return -ERESTARTSYS;
+ timeout = -ERESTARTSYS;
+ break;
}
__set_current_state(state);
spin_unlock_irq(&x->wait.lock);
timeout = schedule_timeout(timeout);
spin_lock_irq(&x->wait.lock);
-
- /*
- * If the completion has arrived meanwhile
- * then return 1 jiffy time left:
- */
- if (x->done && !timeout) {
- timeout = 1;
- break;
- }
-
- if (!timeout) {
- __remove_wait_queue(&x->wait, &wait);
- return timeout;
- }
- } while (!x->done);
+ } while (!x->done && timeout);
__remove_wait_queue(&x->wait, &wait);
+ if (!x->done)
+ return timeout;
}
x->done--;
- return timeout;
+ return timeout ?: 1;
}

static long __sched

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