Subject: Re: [OOPS] 2.6.11 - NMI lockup with CFQ scheduler
From: James Bottomley <James.Bottomley@SteelEye.com>
To: Jens Axboe <axboe@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>, Chris Rankin <rankincj@yahoo.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       SCSI Mailing List <linux-scsi@vger.kernel.org>
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Date: Thu, 07 Apr 2005 09:39:43 -0400
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On Thu, 2005-04-07 at 15:32 +0200, Jens Axboe wrote:
> I think Christophs point is that why add sdev_lock as a pointer, instead
> of just killing it? It's only used in one location, so it's not really
> that confusing (and a comment could fix that).

Because any use of sdev->request_queue->queue_lock would likely succeed
even after we've freed the device and released the queue.  If it's a
pointer and we null it after free and release, then any later use will
trigger an immediate NULL deref oops.

Since we've had so many nasty problems around refcounting, I just would
like to assure myself that we're doing everything correctly (I really
believe we are, but empirical evidence is also nice).

James


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