From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>
Subject: Re: Yet another hot unplug NULL pointer dereference (was Re: status
 of oops in sd_revalidate_disk?)
Date: Thu, 16 Feb 2012 10:04:03 +0900
Message-ID: <4F3C5603.1040108@ce.jp.nec.com>
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To: Bart Van Assche <bvanassche@acm.org>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>, jbottomley@parallels.com, linux-scsi@vger.kernel.org, Huajun Li <huajun.li.lee@gmail.com>, Axel Theilmann <theilmann@pre-sense.de>, linux-kernel@vger.kernel.org
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Hi,

On 02/15/12 20:29, Bart Van Assche wrote:
> On Wed, Feb 15, 2012 at 3:26 AM, Jun'ichi Nomura <j-nomura@ce.jp.nec.com> wrote:
>> I think this patch is good, too.
>> Since QUEUE_FLAG_DEAD is also racy, it is not much different
>> from queuedata check, IMO.
> 
> Are you sure ? As far as I know the block layer takes care of
> synchronizing queue flag modifications against request_fn invocations.

QUEUE_FLAG_DEAD is set outside of queue_lock. So it's racy.
However, it's single directional change and the race is benign
if the driver, who sets QUEUE_FLAG_DEAD, is ready to reject
requests.
q->queuedata is same with that regard.

-- 
Jun'ichi Nomura, NEC Corporation