Re: [PATCH 2/5] dm-mpath: return DM_MAPIO_REQUEUE in case of rq allocation failure

[Ming Lei <ming.lei@redhat.com>]

On Fri, Sep 15, 2017 at 04:06:55PM -0400, Mike Snitzer wrote:
> On Fri, Sep 15 2017 at  1:29pm -0400,
> Bart Van Assche <Bart.VanAssche@wdc.com> wrote:
> 
> > On Sat, 2017-09-16 at 00:44 +0800, Ming Lei wrote:
> > > blk-mq will rerun queue via RESTART after one request is completion,
> > > so not necessary to wait random time for requeuing, it should trust
> > > blk-mq to do it.
> > > 
> > > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > > ---
> > >  drivers/md/dm-mpath.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> > > index 96aedaac2c64..f5a1088a6e79 100644
> > > --- a/drivers/md/dm-mpath.c
> > > +++ b/drivers/md/dm-mpath.c
> > > @@ -505,7 +505,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
> > >  			atomic_inc(&m->pg_init_in_progress);
> > >  			activate_or_offline_path(pgpath);
> > >  		}
> > > -		return DM_MAPIO_DELAY_REQUEUE;
> > > +		return DM_MAPIO_REQUEUE;
> > >  	}
> > >  	clone->bio = clone->biotail = NULL;
> > >  	clone->rq_disk = bdev->bd_disk;
> > 
> > So you are reverting the patch below? Thank you very much.
> > 
> > commit 1c23484c355ec360ca2f37914f8a4802c6baeead
> > Author: Bart Van Assche <bart.vanassche@wdc.com>
> > Date:   Wed Aug 9 11:32:12 2017 -0700
> > 
> >     dm mpath: do not lock up a CPU with requeuing activity
> >     
> >     When using the block layer in single queue mode, get_request()
> >     returns ERR_PTR(-EAGAIN) if the queue is dying and the REQ_NOWAIT
> >     flag has been passed to get_request(). Avoid that the kernel
> >     reports soft lockup complaints in this case due to continuous
> >     requeuing activity.
> >     
> >     Fixes: 7083abbbf ("dm mpath: avoid that path removal can trigger an infinite loop")
> >     Cc: stable@vger.kernel.org
> >     Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> >     Tested-by: Laurence Oberman <loberman@redhat.com>
> >     Reviewed-by: Christoph Hellwig <hch@lst.de>
> >     Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> 
> The problem is that multipath_clone_and_map() is now treated as common
> code (thanks to both blk-mq and old .request_fn now enjoying the use of
> blk_get_request) BUT: Ming please understand that this code is used by
> old .request_fn too.  So it would seem that the use of

Hi Mike,

OK, thanks for pointing this out.

> DM_MAPIO_DELAY_REQUEUE vs DM_MAPIO_REQUEUE needs to be based on dm-sq vs
> dm-mq.

Yeah, just forget that dm-mq can't work on underlying queue which is
block legacy path, also forget the exact reason, :-(

-- 
Ming