From: Bart Van Assche <bvanassche@acm.org>
To: Chanho Min <chanho0207@gmail.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>,
James Bottomley <JBottomley@parallels.com>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] fix NULL-pointer dereference on scsi_run_queue
Date: Tue, 07 Aug 2012 09:30:25 +0000 [thread overview]
Message-ID: <5020E031.9080406@acm.org> (raw)
In-Reply-To: <CAOAMb1BWWzYPSode-6Y9+O5eNhMc-bYofCNwMRmzeC9-nhRb4g@mail.gmail.com>
On 08/07/12 08:53, Chanho Min wrote:
> On Tue, Aug 7, 2012 at 2:56 AM, Bart Van Assche <bvanassche@acm.org> wrote:
>> Indeed. How about the patch below ? Scsi devices are removed from
>> starved_list after blk_cleanup_queue() and before put_device(). That
>> guarantees that inside scsi_run_queue() get_device() under host lock
>> will succeed.
>
> Thanks, IMHO, it's harmless and the simple way to solve this issue.
> But, I think the second half of your patches are not required, extra
> referecne is might suffice?
I'm afraid that without the second half of that patch the following race
is still possible:
- sdev reference count drops to zero while scsi_run_queue() is in
progress and while that sdev is on the starved_list of its SCSI host;
scsi_device_dev_release_usercontext() call is scheduled but not yet
executed.
- scsi_run_queue() takes that sdev off the local starved_list.
- scsi_run_queue() calls get_device() and that call fails since the
sdev reference count is zero.
- scsi_device_dev_release_usercontext() gets scheduled and frees the
sdev.
- scsi_run_queue() proceeds and calls __blk_run_queue() on a freed
queue, which is what we were trying to avoid.
Bart.
next prev parent reply other threads:[~2012-08-07 9:30 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-02 8:41 [PATCH] fix NULL-pointer dereference on scsi_run_queue Chanho Min
2012-08-02 8:57 ` James Bottomley
2012-08-02 9:28 ` Chanho Min
2012-08-02 9:34 ` James Bottomley
2012-08-03 2:28 ` Chanho Min
2012-08-03 3:01 ` Mike Christie
2012-08-04 9:01 ` Bart Van Assche
2012-08-04 16:46 ` Mike Christie
2012-08-04 20:18 ` Bart Van Assche
2012-08-04 22:36 ` Mike Christie
2012-08-06 17:56 ` Bart Van Assche
2012-08-07 8:53 ` Chanho Min
2012-08-07 9:30 ` Bart Van Assche [this message]
2012-08-08 3:42 ` Chanho Min
2012-08-08 7:37 ` Bart Van Assche
2012-08-07 9:43 ` Bart Van Assche
2012-08-07 16:16 ` Mike Christie
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