linux-kernel - Re: Yet another hot unplug NULL pointer dereference (was Re: status of oops in sd_revalidate

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Message-ID: <4F3C5603.1040108@ce.jp.nec.com>
Date:	Thu, 16 Feb 2012 10:04:03 +0900
From:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To:	Bart Van Assche <bvanassche@....org>
CC:	Stefan Richter <stefanr@...6.in-berlin.de>,
	jbottomley@...allels.com, linux-scsi@...r.kernel.org,
	Huajun Li <huajun.li.lee@...il.com>,
	Axel Theilmann <theilmann@...-sense.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Yet another hot unplug NULL pointer dereference (was Re: status
 of oops in sd_revalidate_disk?)

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@...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
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