Re: [PATCH] io stalls

[Nick Piggin]

Andrea Arcangeli wrote:

>On Mon, Jun 09, 2003 at 05:39:23PM -0400, Chris Mason wrote:
>
>>+	if (!waitqueue_active(&q->wait_for_requests[rw]))
>>+		clear_queue_full(q, rw);
>>
>
>you've an smp race above, the smp safe implementation is this:
>
>	if (!waitqueue_active(&q->wait_for_requests[rw])) {
>		clear_queue_full(q, rw);
>		mb();
>		if (unlikely(waitqueue_active(&q->wait_for_requests[rw])))
>			wake_up(&q->wait_for_requests[rw]);
>	}
>
>I'm also unsure what the "waited" logic does, it doesn't seem necessary.
>

When a task is woken up, it is quite likely that the
queue is still marked full.