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

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Date:	Tue, 14 Feb 2012 12:54:42 +0100
From:	Bart Van Assche <bvanassche@....org>
To:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
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?)

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 ?

Bart.
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