linux-kernel - Re: [PATCH] blk-exec-assign-endio-before-queue-dead-check

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Date:	Wed, 6 Jun 2012 23:13:02 -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] blk-exec-assign-endio-before-queue-dead-check

On Wed, Jun 6, 2012 at 10:53 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Thu, Jun 7, 2012 at 2:42 PM, Muthu Kumar <muthu.lkml@...il.com> wrote:
>>>> One more thing to consider is, the completion function is called from
>>>> the same calling context here. As far as my check, it looks ok. Let me
>>>> know if you think otherwise.
>>>
>>> Not sure what you mean.
>>
>> If there is no error, then the completion routine is called in a
>> different context - rq completion context. But here, we call the
>> completion routine in the same context of the caller.
>
> Ah, okay. I think the only problem there would be that the end_io
> callback is being called outside queue lock. Can you please take care
> of that too?
>

Revised patch (below as well as attached)

>> 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.
>
> Yeah, sounds about right.
>
> Thanks.
>
> --
> tejun


-----------------------
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.

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 */

View attachment "blk-exec-assign-endio-before-queue-dead-check.patch" of type "text/x-diff" (1163 bytes)