From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <htejun@gmail.com>
Return-Path: <htejun@gmail.com>
Sender: Tejun Heo <htejun@gmail.com>
Date: Tue, 10 Apr 2018 08:30:31 -0700
From: "tj@kernel.org" <tj@kernel.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"israelr@mellanox.com" <israelr@mellanox.com>,
	"sagi@grimberg.me" <sagi@grimberg.me>, "hch@lst.de" <hch@lst.de>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	"axboe@kernel.dk" <axboe@kernel.dk>,
	"maxg@mellanox.com" <maxg@mellanox.com>
Subject: Re: [PATCH v4] blk-mq: Fix race conditions in request timeout
 handling
Message-ID: <20180410153031.GO3126663@devbig577.frc2.facebook.com>
References: <20180410013455.7448-1-bart.vanassche@wdc.com>
 <20180410084133.GB9133@ming.t460p>
 <b36ea1107be4f32fb04fffdde3ee45a2e0fcc36c.camel@wdc.com>
 <20180410135541.GA22340@ming.t460p>
 <7c4a8b019182d5a9259ef20e6462b3f6a533abed.camel@wdc.com>
 <20180410143007.GB22340@ming.t460p>
 <e2762e359649946543ee22cf6ebf0c08410f7963.camel@wdc.com>
 <20180410152553.GC22340@ming.t460p>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <20180410152553.GC22340@ming.t460p>
List-ID: <linux-block@vger.kernel.org>

Hello, Ming.

On Tue, Apr 10, 2018 at 11:25:54PM +0800, Ming Lei wrote:
> +   if (time_after_eq(jiffies, deadline) &&
> +       blk_mq_change_rq_state(rq, MQ_RQ_IN_FLIGHT, MQ_RQ_COMPLETE)) {
> +       blk_mq_rq_timed_out(rq, reserved);
> 
> Normal completion still can happen between blk_mq_change_rq_state()
> and blk_mq_rq_timed_out().
> 
> In tj's approach, there is synchronize_rcu() between writing aborted_gstate
> and blk_mq_rq_timed_out, it is easier for normal completion to happen during
> the big window.

I don't think plugging this hole is all that difficult, but this
shouldn't lead to any critical failures.  If so, that'd be a driver
bug.

Thanks.

-- 
tejun