Re: [dm-devel] [PATCH] block: Check that queue is alive in blk_insert_cloned_request()

[Alan Stern <stern rowland harvard edu>]

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_.

Alan Stern