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SubjectRe: wait_for_completion_timeout() spurious failure under heavy load?
On 06/20, Ingo Molnar wrote:
>
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4405,6 +4405,16 @@ do_wait_for_common(struct completion *x, long timeout, int 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;

This is the real nitpick, but I wonder what is the right behaviour
of wait_for_completion_timeout(x, 0) when x->done != 0. Perhaps we
can return 1 in that case too, just for the consistency?

IOW, how about the patch below? this also makes the code a bit
simpler because we factor out __remove_wait_queue().

Oleg.

--- kernel/sched.c
+++ kernel/sched.c
@@ -4746,15 +4746,13 @@ do_wait_for_common(struct completion *x,
spin_unlock_irq(&x->wait.lock);
timeout = schedule_timeout(timeout);
spin_lock_irq(&x->wait.lock);
- 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 0;
}
x->done--;
- return timeout;
+ return timeout ?: 1;
}

static long __sched


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