linux-kernel - Re: [PATCH] block: Check that queue is alive in blk_insert_cloned

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Date:	Mon, 11 Jul 2011 20:52:36 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mike Snitzer <snitzer@...hat.com>
cc:	Roland Dreier <roland@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	<linux-scsi@...r.kernel.org>,
	Steffen Maier <maier@...ux.vnet.ibm.com>,
	"Manvanthara B. Puttashankar" <manvanth@...ux.vnet.ibm.com>,
	Tarak Reddy <tarak.reddy@...ibm.com>,
	"Seshagiri N. Ippili" <sesh17@...ux.vnet.ibm.com>,
	<linux-kernel@...r.kernel.org>,
	device-mapper development <dm-devel@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] block: Check that queue is alive in blk_insert_cloned_request()

On Mon, 11 Jul 2011, Mike Snitzer wrote:

> [cc'ing dm-devel, vivek and tejun]
> 
> On Fri, Jul 8, 2011 at 7:04 PM, Roland Dreier <roland@...nel.org> wrote:
> > From: Roland Dreier <roland@...estorage.com>
> >
> > This fixes crashes such as the below that I see when the storage
> > underlying a dm-multipath device is hot-removed.  The problem is that
> > dm requeues a request to a device whose block queue has already been
> > cleaned up, and blk_insert_cloned_request() doesn't check if the queue
> > is alive, but rather goes ahead and tries to queue the request.  This
> > ends up dereferencing the elevator that was already freed in
> > blk_cleanup_queue().
> 
> Your patch looks fine to me:
> Acked-by: Mike Snitzer <snitzer@...hat.com>

There's still the issue that Stefan Richter pointed out: The test for a 
dead queue must be made _after_ acquiring the queue lock, not _before_.

Alan Stern

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