[dm-devel] dm: fix blk-mq request-based DM queue initialization

[Christoph Hellwig]

On Wed, Apr 29, 2015 at 09:41:52PM -0400, Mike Snitzer wrote:
> > I'm not quite up to speed with this area of code, but shouldn't
> > we always tear the queue fully down before trying to reinitialize it?
> 
> No, the same request_queue should be used for the lifetime of a DM
> device.
> 
> I'm not interested in reinitializing the queue.  A DM table reload has
> no need to destroy and recreate the request_queue associated with 
> the DM device.  It would be bad to do so too because we actually use the
> queue across table reloads in the case of dm-multipath with no paths
> (see: map_request's handling of DM_MAPIO_REQUEUE which triggers
> dm_requeue_request).

Well - we're obviously trying to reinitialize it here and only error
out very low level with your patch.  What I mean is that we shouldn't
even try to reinitialize it at a much higher level, so we don't need
this blk-mq specific hack down here.