linux-kernel - Re: [PATCH] block: In blk_execute_rq_nowait, init rq->end

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Message-ID: <CAFR8uedpGWgOzvGkFAhjMdEM__RdPQSvYYX99pEmPgoXaB0UAA@mail.gmail.com>
Date:	Fri, 8 Jun 2012 08:37:41 -0700
From:	Muthu Kumar <muthu.lkml@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	James.Bottomley@...senpartnership.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: In blk_execute_rq_nowait, init rq->end_io before
 checking for dead queue.

Tejun, Jens,
This is a real problem, right? Should we fix it differently?

Regards,
Muthu

On Wed, Jun 6, 2012 at 11:27 PM, Muthu Kumar <muthu.lkml@...il.com> wrote:
> On Wed, Jun 6, 2012 at 11:16 PM, Tejun Heo <tj@...nel.org> wrote:
>> Sorry to be nit-picky but Jens would appreciate proper subject and it
>> would also be nice to mention the locking change (or even separate
>> that into a separate patch).
>
> No problem. Changed the subject and also added the info about queue
> lock in the description. Please check.
>
> -----------------------
> blk-exec.c: In blk_execute_rq_nowait(), if the queue is dead, call to
> done() routine is not made. That will result in blk_execute_rq() stuck
> in wait_for_completion(). Avoid this by initializing rq->end_io to
> done() routine before we check for dead queue.
>
> Also, in case of dead queue, call the completion routine with queue->lock held.
>
>
> Signed-off-by: Muthukumar Ratty <muthur@...il.com>
> CC: Tejun Heo <tj@...nel.org>
> CC: Jens Axboe <axboe@...nel.dk>
> CC: James Bottomley <James.Bottomley@...senpartnership.com>
>
> -----------------------
>
> diff --git a/block/blk-exec.c b/block/blk-exec.c
> index fb2cbd5..284bf56 100644
> --- a/block/blk-exec.c
> +++ b/block/blk-exec.c
> @@ -53,16 +53,17 @@ void blk_execute_rq_nowait(struct request_queue
> *q, struct gendisk *bd_disk,
>        WARN_ON(irqs_disabled());
>        spin_lock_irq(q->queue_lock);
>
> +       rq->rq_disk = bd_disk;
> +       rq->end_io = done;
> +
>        if (unlikely(blk_queue_dead(q))) {
> -               spin_unlock_irq(q->queue_lock);
>                rq->errors = -ENXIO;
>                if (rq->end_io)
>                        rq->end_io(rq, rq->errors);
> +               spin_unlock_irq(q->queue_lock);
>                return;
>        }
>
> -       rq->rq_disk = bd_disk;
> -       rq->end_io = done;
>        __elv_add_request(q, rq, where);
>        __blk_run_queue(q);
>        /* the queue is stopped so it won't be run */
>
>
> ------------------------------------
>
>
>
>
>
>
>
>>
>> Thanks.
>>
>> --
>> tejun
--
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