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From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "tom.leiming@gmail.com" <tom.leiming@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"hch@infradead.org" <hch@infradead.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"yizhan@redhat.com" <yizhan@redhat.com>,
	"axboe@fb.com" <axboe@fb.com>, "tj@kernel.org" <tj@kernel.org>
Subject: Re: [PATCH v1 3/3] blk-mq: start to freeze queue just after setting dying
Date: Fri, 17 Mar 2017 20:36:58 +0000	[thread overview]
Message-ID: <1489783004.2826.13.camel@sandisk.com> (raw)
In-Reply-To: <CACVXFVPF0Sx5HyU+xw0MyghYMWifZ0SDH0YCtM-jrhieOJOJGg@mail.gmail.com>

On Sat, 2017-03-18 at 02:32 +0800, Ming Lei wrote:
> On Sat, Mar 18, 2017 at 1:32 AM, Bart Van Assche wrote:
> > +       /*
> > +        * Avoid that the updates of the queue flags and q_usage_counte=
r
> > +        * are reordered.
> > +        */
> > +       smp_wmb();
>=20
> atomic_inc_return() in blk_mq_freeze_queue_start() does imply a
> barrier(smp_mb()).

Hello Ming,

It's probably a good idea to mention that in a comment. The implementation
of blk_mq_freeze_queue_start() namely could be changed in the future such
that it uses another atomic operation that doesn't implicitly perform smp_m=
b().

Thanks,

Bart.=

WARNING: multiple messages have this Message-ID (diff)
From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "tom.leiming@gmail.com" <tom.leiming@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"hch@infradead.org" <hch@infradead.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"yizhan@redhat.com" <yizhan@redhat.com>,
	"axboe@fb.com" <axboe@fb.com>, "tj@kernel.org" <tj@kernel.org>
Subject: Re: [PATCH v1 3/3] blk-mq: start to freeze queue just after setting dying
Date: Fri, 17 Mar 2017 20:36:58 +0000	[thread overview]
Message-ID: <1489783004.2826.13.camel@sandisk.com> (raw)
In-Reply-To: <CACVXFVPF0Sx5HyU+xw0MyghYMWifZ0SDH0YCtM-jrhieOJOJGg@mail.gmail.com>

On Sat, 2017-03-18 at 02:32 +0800, Ming Lei wrote:
> On Sat, Mar 18, 2017 at 1:32 AM, Bart Van Assche wrote:
> > +       /*
> > +        * Avoid that the updates of the queue flags and q_usage_counter
> > +        * are reordered.
> > +        */
> > +       smp_wmb();
> 
> atomic_inc_return() in blk_mq_freeze_queue_start() does imply a
> barrier(smp_mb()).

Hello Ming,

It's probably a good idea to mention that in a comment. The implementation
of blk_mq_freeze_queue_start() namely could be changed in the future such
that it uses another atomic operation that doesn't implicitly perform smp_mb().

Thanks,

Bart.

  reply	other threads:[~2017-03-17 20:39 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-17  9:57 [PATCH v1 0/3] blk-mq: dying queue fix & improvement Ming Lei
2017-03-17  9:57 ` [PATCH v1 1/3] blk-mq: don't complete un-started request in timeout handler Ming Lei
2017-03-18 11:24   ` Hannes Reinecke
2017-03-18 11:24     ` Hannes Reinecke
2017-03-17  9:57 ` [PATCH v1 2/3] blk-mq: comment on races related with " Ming Lei
2017-03-17 17:39   ` Bart Van Assche
2017-03-17 17:39     ` Bart Van Assche
2017-03-17 18:23     ` Ming Lei
2017-03-18 11:25   ` Hannes Reinecke
2017-03-18 11:25     ` Hannes Reinecke
2017-03-17  9:57 ` [PATCH v1 3/3] blk-mq: start to freeze queue just after setting dying Ming Lei
2017-03-17 17:32   ` Bart Van Assche
2017-03-17 17:32     ` Bart Van Assche
2017-03-17 18:32     ` Ming Lei
2017-03-17 20:36       ` Bart Van Assche [this message]
2017-03-17 20:36         ` Bart Van Assche
2017-03-17 23:26   ` Bart Van Assche
2017-03-17 23:26     ` Bart Van Assche
2017-03-18  1:01     ` Ming Lei
2017-03-18 11:27   ` Hannes Reinecke
2017-03-18 11:27     ` Hannes Reinecke

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