From: Mike Snitzer <snitzer@redhat.com>
To: Bart Van Assche <Bart.VanAssche@sandisk.com>
Cc: "axboe@kernel.dk" <axboe@kernel.dk>,
device-mapper development <dm-devel@redhat.com>,
"hch@lst.de" <hch@lst.de>
Subject: Re: [PATCH 8/9] dm: Fix two race conditions related to stopping and starting queues
Date: Thu, 1 Sep 2016 11:05:03 -0400 [thread overview]
Message-ID: <20160901150503.GA11074@redhat.com> (raw)
In-Reply-To: <BLUPR02MB1683D3D8F604FEB429143A4381E20@BLUPR02MB1683.namprd02.prod.outlook.com>
On Thu, Sep 01 2016 at 10:23am -0400,
Bart Van Assche <Bart.VanAssche@sandisk.com> wrote:
> On 08/31/16 20:14, Mike Snitzer wrote:
> > On Wed, Aug 31 2016 at 6:18pm -0400,
> > Bart Van Assche <bart.vanassche@sandisk.com> wrote:
> >
> >> Ensure that all ongoing dm_mq_queue_rq() and dm_mq_requeue_request()
> >> calls have stopped before setting the "queue stopped" flag. This
> >> allows to remove the "queue stopped" test from dm_mq_queue_rq() and
> >> dm_mq_requeue_request(). Use BLK_MQ_S_STOPPED instead of
> >> QUEUE_FLAG_STOPPED.
> >
> > At first glance, at a minimum this patch needs a better header. It
> > seems you're doing 2 things:
> >
> > 1) using blk_mq_{freeze,unfreeze}_queue() actually makes dm_stop_queue()
> > work for blk-mq? Whereby fixing blk-mq race(s)?
> >
> > 2) switching away from QUEUE_FLAG_STOPPED to BLK_MQ_S_STOPPED (via
> > blk_mq_queue_stopped)
> > - not clear to me that dm-mq's use of QUEUE_FLAG_STOPPED wasn't fine;
> > NVMe also uses it for blk-mq
>
> Hello Mike,
>
> Adding the blk_mq_{freeze,unfreeze}_queue() calls is indeed what fixes
> the race conditions related to stopping dm queues and what makes
> dm_stop_queue() work.
OK, thanks for confirming.
> If other blk-mq users and developers agree that QUEUE_FLAG_STOPPED
> should be set for stopped blk-mq queues then I think the code to set
> that flag should be moved into the blk-mq core. However, setting that
> flag for blk-mq queues seems redundant to me. Hence my proposal to
> introduce blk_mq_queue_stopped() instead.
This is a secondary issue that can be dealt with independent of the rest
of your DM patchset.
I've staged most of your changes (with slight tweaks), see:
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.9
Only remaining issue is the queue dying race(s) in dm-multipath.
next prev parent reply other threads:[~2016-09-01 15:05 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-31 22:14 [PATCH 0/9] dm patches for kernel v4.9 Bart Van Assche
2016-08-31 22:15 ` [PATCH 1/9] blk-mq: Introduce blk_mq_queue_stopped() Bart Van Assche
2016-08-31 22:16 ` [PATCH 2/9] dm: Rename a function argument Bart Van Assche
2016-09-01 3:29 ` Mike Snitzer
2016-09-01 14:17 ` Bart Van Assche
2016-08-31 22:16 ` [PATCH 3/9] dm: Introduce signal_pending_state() Bart Van Assche
2016-08-31 22:16 ` [PATCH 4/9] dm: Convert wait loops Bart Van Assche
2016-08-31 22:17 ` [PATCH 5/9] dm: Add two lockdep_assert_held() statements Bart Van Assche
2016-08-31 22:17 ` [PATCH 6/9] dm: Simplify dm_old_stop_queue() Bart Van Assche
2016-08-31 22:17 ` [PATCH 7/9] dm: Mark block layer queue dead before destroying the dm device Bart Van Assche
2016-08-31 22:18 ` [PATCH 8/9] dm: Fix two race conditions related to stopping and starting queues Bart Van Assche
2016-09-01 3:13 ` Mike Snitzer
2016-09-01 14:23 ` Bart Van Assche
2016-09-01 15:05 ` Mike Snitzer [this message]
2016-09-01 15:31 ` Bart Van Assche
2016-09-01 15:50 ` Mike Snitzer
2016-09-01 16:12 ` Mike Snitzer
2016-09-01 17:59 ` Bart Van Assche
2016-09-01 19:05 ` Mike Snitzer
2016-09-01 19:35 ` Mike Snitzer
2016-09-01 20:15 ` Bart Van Assche
2016-09-01 20:33 ` Mike Snitzer
2016-09-01 20:39 ` Bart Van Assche
2016-09-01 20:48 ` Mike Snitzer
2016-09-01 20:52 ` Bart Van Assche
2016-09-01 21:17 ` Mike Snitzer
2016-09-01 22:18 ` Mike Snitzer
2016-09-01 22:22 ` Bart Van Assche
2016-09-01 22:26 ` Mike Snitzer
2016-09-01 23:17 ` Bart Van Assche
2016-09-01 23:47 ` Mike Snitzer
2016-09-02 0:03 ` Bart Van Assche
2016-09-02 15:12 ` Mike Snitzer
2016-09-02 16:10 ` should blk-mq halt requeue processing while queue is frozen? [was: Re: [PATCH 8/9] dm: Fix two race conditions related to stopping and starting queues] Mike Snitzer
2016-09-02 22:42 ` [dm-devel] should blk-mq halt requeue processing while queue is frozen? Bart Van Assche
2016-09-03 0:34 ` Mike Snitzer
2016-09-07 16:41 ` Mike Snitzer
2016-09-13 8:01 ` [dm-devel] " Bart Van Assche
2016-09-13 14:36 ` Mike Snitzer
2016-08-31 22:18 ` [PATCH 9/9] dm path selector: Avoid that device removal triggers an infinite loop Bart Van Assche
2016-09-01 2:49 ` Mike Snitzer
2016-09-01 14:14 ` Bart Van Assche
2016-09-01 15:06 ` Mike Snitzer
2016-09-01 15:22 ` Bart Van Assche
2016-09-01 15:26 ` Mike Snitzer
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