linux-kernel - Re: [PATCH] fix NULL-pointer dereference on scsi_run

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Message-ID: <CAOAMb1C=fk_Ejm6TwOhoNLhP1TyRJ+QVi93VaqUmxoHsM1iXtQ@mail.gmail.com>
Date:	Thu, 2 Aug 2012 18:28:21 +0900
From:	Chanho Min <chanho0207@...il.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] fix NULL-pointer dereference on scsi_run_queue

On Thu, Aug 2, 2012 at 5:57 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Thu, 2012-08-02 at 17:41 +0900, Chanho Min wrote:
>> This patch is to fix a oops from a torn down device. When
>> scsi_run_queue process starved queues, scsi_request_fn can race with
>> scsi_remove_device. In this case, rarely, scsi_request_fn release the
>> last reference and set sdev->request_queue to NULL. It result in
>> NULL-pointer dereference when spin_unlock is tried with (NULL)->
>> queue_lock. We need to add an extra reference to the device on both
>> sides of the __blk_run_queue to hold reference until scsi_request_fn
>> is finished.
>
> You need a recent kernel with this patch:
>
> commit 940f5d47e2f2e1fa00443921a0abf4822335b54d
> Author: Bart Van Assche <bvanassche@....org>
> Date:   Fri Jun 29 15:34:26 2012 +0000
>
>     [SCSI] Avoid dangling pointer in scsi_requeue_command()
>
> James
It is different from my case. This is occured inside scsi_run_queue
and on processing starved_list.
Another sdev is obtained from starved_list.
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