linux-kernel - Re: [PATCH 10/10] block: fix request_queue lifetime handling by making blk_queue

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Date:	Wed, 19 Oct 2011 10:33:37 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, ctalbott@...gle.com
Subject: Re: [PATCH 10/10] block: fix request_queue lifetime handling by
 making blk_queue_cleanup() proper shutdown

Hello,

On Wed, Oct 19, 2011 at 01:29:14PM -0400, Vivek Goyal wrote:
> > Hmmm... the thing is you need to check DEAD again once after releasing
> > and re-grabbing the queuelock, os if we move the test into the caller,
> > we end up having one in the caller and one in the callee, so I thought
> > it would be better to keep them in the same function.
> 
> Sorry I did not get that why do we need to check again for DEAD after
> realeasing the queue lock. From throttling perspective, we grab lock
> once, if queue is DEAD, release lock and just return.
> 
> blk_throtl_bio() {
> 
>   bunch_of_checks_without_queue_lock;
> 
>   spin_lock()
>   if (queue_dead) {
> 	spin_unlock()
> 	return;
>   }
> 
>   throtl_get_tg();
> }	

Because DEAD state is protected by queue_lock and get_tg may release
and re-grab queue_lock across allocation?  It needs to re-test after
re-grabbing.

Thanks.

-- 
tejun
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