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SubjectRe: [PATCH] block: Avoid missed wakeup in request waitqueue
On Mon, May 28, 2012 at 12:19:03PM +0800, Asias He wrote:
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 1f61b74..1a45877 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -359,9 +359,10 @@ EXPORT_SYMBOL(blk_put_queue);
> */
> void blk_drain_queue(struct request_queue *q, bool drain_all)
> {
> + int i;
> +
> while (true) {
> bool drain = false;
> - int i;
>
> spin_lock_irq(q->queue_lock);
>
> @@ -400,6 +401,14 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
> break;
> msleep(10);
> }
> +
> + /* Wake up threads which are sleeping on get_request() */
> + spin_lock_irq(q->queue_lock);
> + for (i = 0; i < ARRAY_SIZE(q->rq.wait); i++) {
> + if (waitqueue_active(&q->rq.wait[i]))
> + wake_up_all(&q->rq.wait[i]);
> + }
> + spin_unlock_irq(q->queue_lock);

I don't think we need waitqueue_active() optimization here. Let's
just do,

/* please explain why this is necessary */
for (i = 0; i < ARRAY_SIZE(q->rq.wait); i++)
wake_up_all(&q->rq.wait[i]);

Thanks.

--
tejun


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