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

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Message-ID: <20120214143800.69703df9@stein>
Date:	Tue, 14 Feb 2012 14:38:00 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Bart Van Assche <bvanassche@....org>
Cc:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
	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?)

On Feb 14 Bart Van Assche wrote:
> On Tue, Feb 14, 2012 at 12:34 PM, Jun'ichi Nomura
> <j-nomura@...jp.nec.com> wrote:
> > While scsi_device is propery refcounted object,
> > q->queuedata is set to NULL by scsi_remove_device() asynchronously.
> > So every reader of scsi_device's q->queuedata should always check it.
> 
> As far as I can see this patch narrows the race window but doesn't fix
> the race. At least sd_prep_fn() still reads queuedata and if I'm not
> mistaken that read races with scsi_remove_device(). Has it been
> considered to modify scsi_remove_device() and scsi_request_fn() such
> that device removal is communicated from the former to the latter in
> another way than by clearing queuedata ?

Or asked differently, *what* is supposed to serialize the ->queuedata
accesses?

(If it is the BKL -- well, some bleeding edge kernel versions lack it,
sources say.)
-- 
Stefan Richter
-=====-===-- --=- -===-
http://arcgraph.de/sr/
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