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

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Message-ID: <501DA3F0.4090009@cs.wisc.edu>
Date:	Sat, 04 Aug 2012 17:36:32 -0500
From:	Mike Christie <michaelc@...wisc.edu>
To:	Bart Van Assche <bvanassche@....org>
CC:	Chanho Min <chanho0207@...il.com>,
	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

On 08/04/2012 03:18 PM, Bart Van Assche wrote:
> On 08/04/12 16:46, Mike Christie wrote:
>> I think we have to have scsi-ml do a get_device when a sdev is added to
>> the starved entry and then do a put_device when it is removed (must do
>> these under the host lock for the starved entry case too). I am not sure
>> if that is just a hack/papering-over of the problem and there are more
>> issues like this.
> 
> That would result in a more complex patch than the patch at the start of
> this thread, isn't it ? Also, IMHO it would help to document which

Yaah, but the original patch in this thread is still racey isn't it?

 		spin_unlock(shost->host_lock);

The sdev/queue could get freed by some other thread when this function
is right here, so the get_device call is now going to try to access
freed memory.


+		/* hold a reference on the device so it doesn't release device */
+		get_device(&sdev->sdev_gendev);


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