Re: [PATCH] io stalls

Andrea Arcangeli
2003-06-11T00:54:08Z

On Wed, Jun 11, 2003 at 10:48:23AM +1000, Nick Piggin wrote:
>
>
> 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.

but we don't care if it's marked full, see __get_request. If we cared
about full it would deadlock anyways (no matter the waited logic)

Andrea