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

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Date:	Mon, 11 Jul 2011 21:22:06 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Alan Stern <stern@...land.harvard.edu>
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>,
	jaxboe@...ionio.com
Subject: Re: block: Check that queue is alive in blk_insert_cloned_request()

On Mon, Jul 11 2011 at  8:52pm -0400,
Alan Stern <stern@...land.harvard.edu> wrote:

> 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_.

Yes, quite important.

Jens, can you tweak the patch or should Roland send a v2?
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