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From: Tejun Heo <tj@kernel.org>
To: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Sagi Grimberg <sagi@grimberg.me>,
	Israel Rukshin <israelr@mellanox.com>,
	Max Gurtovoy <maxg@mellanox.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] blk-mq: Fix recently introduced races in the timeout handling code
Date: Mon, 9 Apr 2018 09:47:37 -0700	[thread overview]
Message-ID: <20180409164737.GE3126663@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <20180409052038.5391-1-bart.vanassche@wdc.com>

Hey, Bart.

On Sun, Apr 08, 2018 at 10:20:38PM -0700, Bart Van Assche wrote:
> If a completion occurs after blk_mq_rq_timed_out() has reset
> rq->aborted_gstate and the request is again in flight when the timeout
> expires then a request will be completed twice: a first time by the
> timeout handler and a second time when the regular completion occurs.

Are we still talking about the same BLK_EH_RESET_TIMER case?  This can
be solved by the two patches which rcu-synchronizes the hand-over to
normal completion path, right?

> Additionally, the blk-mq timeout handling code ignores completions that
> occur after blk_mq_check_expired() has been called and before
> blk_mq_rq_timed_out() has reset rq->aborted_gstate. If a block driver
> timeout handler always returns BLK_EH_RESET_TIMER then the result will
> be that the request never terminates.

And this is the same race window which was always there, right?  I
really don't think reducing or closing this window requires full
synchronization.

Thanks.

-- 
tejun

  parent reply	other threads:[~2018-04-09 16:47 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-09  5:20 [PATCH] blk-mq: Fix recently introduced races in the timeout handling code Bart Van Assche
2018-04-09  8:37 ` Sagi Grimberg
2018-04-09 14:37   ` Bart Van Assche
2018-04-09 14:37     ` Bart Van Assche
2018-04-09 15:42   ` Israel Rukshin
2018-04-09 16:49   ` Tejun Heo
2018-04-09  9:37 ` Christoph Hellwig
2018-04-09 14:58   ` Bart Van Assche
2018-04-09 14:58     ` Bart Van Assche
2018-04-09 15:03     ` Jens Axboe
2018-04-09 16:47 ` Tejun Heo [this message]
2018-04-09 17:03   ` Bart Van Assche
2018-04-09 17:03     ` Bart Van Assche
2018-04-09 18:56     ` tj
2018-04-09 21:30       ` Bart Van Assche
2018-04-09 21:30         ` Bart Van Assche
2018-04-09 21:40         ` tj
  -- strict thread matches above, loose matches on Subject: below --
2018-04-10 15:37 Alex G.
2018-04-10 15:37 ` Alex G.

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