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

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Date:	Fri, 3 Aug 2012 11:28:43 +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

> Does it occur with that patch applied?
I'm trying to reproduce it with that patch. but, It is unlikely to be fixed.
because scsi_run_queue is invoked from scsi_requeue_run_queue,
not scsi_requeue_command.

> If it does, the likely fix would be to take a copy of the queue ... but
> I'd like to understand why first.  An active command has an automatic
> reference to the sdev_gendev, so it shouldn't be the normal case.  This
> was broken by unprep because it releases the command from the queue and
> drops the reference.  We may have another case like unjprep, but in that
__scsi_remove_device drops the last reference under race condition.

> case, we need to find it ... trying to add extra get/put_device() calls
> will paper over the problem.
yes, extra reference is not good to fix.
But, As long as scsi_device_dev_release_usercontext set request_queue
to NULL, Isn't it necessary to ensure that __blk_run_queue don't release device?

Thanks a lot!
Chanho Min
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