Re: block: Check that queue is alive in blk_insert_cloned_request()

[Mike Snitzer <snitzer@redhat.com>]

On Mon, Jul 11 2011 at  8:52pm -0400,
Alan Stern <stern@rowland.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@kernel.org> wrote:
> > > From: Roland Dreier <roland@purestorage.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@redhat.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?