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

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Date:	Wed, 8 Aug 2012 12:42:44 +0900
From:	Chanho Min <chanho0207@...il.com>
To:	Bart Van Assche <bvanassche@....org>
Cc:	Mike Christie <michaelc@...wisc.edu>,
	James Bottomley <JBottomley@...allels.com>,
	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

> 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.
Thank you for the explanation. It look correct. Let's check one more thing.
What If __scsi_remove_device doesn't release device? : reference count
is more than 2.
So We lost starved_list but device is exist. Is there any issue about this?

Chanho,
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