From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: v3.15 dm-mpath regression: cable pull test causes
	I/O hang
Date: Wed, 2 Jul 2014 18:02:23 -0400
Message-ID: <20140702220223.GA23894@redhat.com>
References: <53AD6B62.2020407@acm.org>
 <20140627133345.GA6150@redhat.com>
Reply-To: device-mapper development <dm-devel@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <dm-devel-bounces@redhat.com>
Content-Disposition: inline
In-Reply-To: <20140627133345.GA6150@redhat.com>
List-Unsubscribe: <https://www.redhat.com/mailman/options/dm-devel>,
	<mailto:dm-devel-request@redhat.com?subject=unsubscribe>
List-Archive: <https://www.redhat.com/archives/dm-devel>
List-Post: <mailto:dm-devel@redhat.com>
List-Help: <mailto:dm-devel-request@redhat.com?subject=help>
List-Subscribe: <https://www.redhat.com/mailman/listinfo/dm-devel>,
	<mailto:dm-devel-request@redhat.com?subject=subscribe>
Sender: dm-devel-bounces@redhat.com
Errors-To: dm-devel-bounces@redhat.com
To: Bart Van Assche <bvanassche@acm.org>
Cc: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>, device-mapper development <dm-devel@redhat.com>
List-Id: dm-devel.ids

On Fri, Jun 27 2014 at  9:33am -0400,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Fri, Jun 27 2014 at  9:02am -0400,
> Bart Van Assche <bvanassche@acm.org> wrote:
> 
> > Hello,
> > 
> > While running a cable pull simulation test with dm_multipath on top of
> > the SRP initiator driver I noticed that after a few iterations I/O locks
> > up instead of dm_multipath processing the path failure properly (see also
> > below for a call trace). At least kernel versions 3.15 and 3.16-rc2 are
> > vulnerable. This issue does not occur with kernel 3.14. I have tried to
> > bisect this but gave up when I noticed that I/O locked up completely with
> > a kernel built from git commit ID e809917735ebf1b9a56c24e877ce0d320baee2ec
> > (dm mpath: push back requests instead of queueing). But with the bisect I
> > have been able to narrow down this issue to one of the patches in "Merge
> > tag 'dm-3.15-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/
> > device-mapper/linux-dm". Does anyone have a suggestion how to analyze this
> > further or how to fix this ?

I still don't have a _known_ fix for your issue but I reviewed commit
e809917735ebf1b9a56c24e877ce0d320baee2ec closer and identified what
looks to be a regression in logic for multipath_busy, it now calls
!pg_ready() instead of directly checking pg_init_in_progress.  I think
this is needed (Hannes, what do you think?):

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 3f6fd9d..561ead6 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -373,7 +373,7 @@ static int __must_push_back(struct multipath *m)
 		 dm_noflush_suspending(m->ti)));
 }
 
-#define pg_ready(m) (!(m)->queue_io && !(m)->pg_init_required)
+#define pg_ready(m) (!(m)->queue_io && !(m)->pg_init_required && !(m)->pg_init_in_progress)
 
 /*
  * Map cloned requests