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

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Date:	Wed, 6 Jun 2012 22:42:49 -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 10:37 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Thu, Jun 7, 2012 at 2:35 PM, Muthu Kumar <muthu.lkml@...il.com> wrote:
>>> Looks like the bug there is rq->rq_disk and rq->end_io assignments
>>> happening after the queue_dead check.  Just move the two lines before
>>> queue_head check?
>>
>> Thought about that. But the problem is, original rq->end_io is not
>> saved before the new assignment. But exploring further, I guess its ok
>> in this use case.
>
> It's supposed to be overridden, so I don't think that matters.

Agree.

>
>> 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.

>
>> Anyway, patch attached (as well as inline).
>>
>> Regards,
>> Muthu
>>
>> -----------------------
>> blk-exec.c: In blk_execute_rq_nowait(), assign rq->endio,rq_disk
>> before queue dead check.
>
> Needs way more description.
>

Let me try.

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.



> Thanks.
>
> --
> tejun
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