Re: [RFC PATCH 2/5] block: Do not stop draining if waitqueue is not empty.

[Tejun Heo <tj@kernel.org>]

On Mon, May 21, 2012 at 05:08:30PM +0800, Asias He wrote:
> If there are processes still in the wait queue, keep draining,
> otherwise these processes would be in D state forever.
> 
> I noticed this situation:
> q->rq.count[0] == 0, q->rq.count[1] == 0, however wait queue
> q->rq.wait[0].task_list and q->rq.wait[1].task_list are not empty.
> 
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: linux-fsdevel@vger.kernel.org
> Signed-off-by: Asias He <asias@redhat.com>
> ---
>  block/blk-core.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ca42fd7..2c2b585 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -394,6 +394,7 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
>  				drain |= q->rq.count[i];
>  				drain |= q->in_flight[i];
>  				drain |= !list_empty(&q->flush_queue[i]);
> +				drain |= waitqueue_active(&q->rq.wait[i]);

Hmm... how does that happen?  What do you mean "you noticed this
situation"?  Did that actually happen or you noticed such scenarios
would be possible?  If rl.wait[] isn't empty with zero rq count, the
queue would hang, so we should be fixing that situation instead of
working around it from cleanup_queue.

Thanks.

-- 
tejun