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From: Keith Busch <keith.busch@intel.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Jianchao Wang <jianchao.w.wang@oracle.com>,
	Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	linux-nvme@lists.infradead.org
Subject: Re: [PATCH 1/2] nvme: pci: simplify timeout handling
Date: Tue, 8 May 2018 09:30:38 -0600	[thread overview]
Message-ID: <20180508153038.GA30842@localhost.localdomain> (raw)
In-Reply-To: <20180428035015.GB5657@ming.t460p>

On Sat, Apr 28, 2018 at 11:50:17AM +0800, Ming Lei wrote:
> This sync may be raced with one timed-out request, which may be handled
> as BLK_EH_HANDLED or BLK_EH_RESET_TIMER, so the above sync queues can't
> work reliably. 

Ming,

As proposed, that scenario is impossible to encounter. Resetting the
controller inline with the timeout reaps all the commands, and then
sets the controller state to RESETTING. While blk-mq may not allow the
driver to complete those requests, having the driver sync with the queues
will hold the controller in the reset state until blk-mq is done with
its timeout work; therefore, it is impossible for the NVMe driver to
return "BLK_EH_RESET_TIMER", and all commands will be completed through
nvme_timeout's BLK_EH_HANDLED exactly as desired.

Could you please recheck my suggestion? The alternatives proposed are
far too risky for a 4.17 consideration, and I'm hoping we can stabilize
this behavior in the current release if possible.

Thanks,
Keith

WARNING: multiple messages have this Message-ID (diff)
From: keith.busch@intel.com (Keith Busch)
Subject: [PATCH 1/2] nvme: pci: simplify timeout handling
Date: Tue, 8 May 2018 09:30:38 -0600	[thread overview]
Message-ID: <20180508153038.GA30842@localhost.localdomain> (raw)
In-Reply-To: <20180428035015.GB5657@ming.t460p>

On Sat, Apr 28, 2018@11:50:17AM +0800, Ming Lei wrote:
> This sync may be raced with one timed-out request, which may be handled
> as BLK_EH_HANDLED or BLK_EH_RESET_TIMER, so the above sync queues can't
> work reliably. 

Ming,

As proposed, that scenario is impossible to encounter. Resetting the
controller inline with the timeout reaps all the commands, and then
sets the controller state to RESETTING. While blk-mq may not allow the
driver to complete those requests, having the driver sync with the queues
will hold the controller in the reset state until blk-mq is done with
its timeout work; therefore, it is impossible for the NVMe driver to
return "BLK_EH_RESET_TIMER", and all commands will be completed through
nvme_timeout's BLK_EH_HANDLED exactly as desired.

Could you please recheck my suggestion? The alternatives proposed are
far too risky for a 4.17 consideration, and I'm hoping we can stabilize
this behavior in the current release if possible.

Thanks,
Keith

  parent reply	other threads:[~2018-05-08 15:28 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-26 12:39 [PATCH 0/2] nvme: pci: fix & improve timeout handling Ming Lei
2018-04-26 12:39 ` Ming Lei
2018-04-26 12:39 ` [PATCH 1/2] nvme: pci: simplify " Ming Lei
2018-04-26 12:39   ` Ming Lei
2018-04-26 15:07   ` jianchao.wang
2018-04-26 15:07     ` jianchao.wang
2018-04-26 15:57     ` Ming Lei
2018-04-26 15:57       ` Ming Lei
2018-04-26 16:16       ` Ming Lei
2018-04-26 16:16         ` Ming Lei
2018-04-27  1:37       ` jianchao.wang
2018-04-27  1:37         ` jianchao.wang
2018-04-27 14:57         ` Ming Lei
2018-04-27 14:57           ` Ming Lei
2018-04-28 14:00           ` jianchao.wang
2018-04-28 14:00             ` jianchao.wang
2018-04-28 21:57             ` Ming Lei
2018-04-28 21:57               ` Ming Lei
2018-04-28 22:27               ` Ming Lei
2018-04-28 22:27                 ` Ming Lei
2018-04-29  1:36                 ` Ming Lei
2018-04-29  1:36                   ` Ming Lei
2018-04-29  2:21                   ` jianchao.wang
2018-04-29  2:21                     ` jianchao.wang
2018-04-29 14:13                     ` Ming Lei
2018-04-29 14:13                       ` Ming Lei
2018-04-27 17:51   ` Keith Busch
2018-04-27 17:51     ` Keith Busch
2018-04-28  3:50     ` Ming Lei
2018-04-28  3:50       ` Ming Lei
2018-04-28 13:35       ` Keith Busch
2018-04-28 13:35         ` Keith Busch
2018-04-28 14:31         ` jianchao.wang
2018-04-28 14:31           ` jianchao.wang
2018-04-28 21:39         ` Ming Lei
2018-04-28 21:39           ` Ming Lei
2018-04-30 19:52           ` Keith Busch
2018-04-30 19:52             ` Keith Busch
2018-04-30 23:14             ` Ming Lei
2018-04-30 23:14               ` Ming Lei
2018-05-08 15:30       ` Keith Busch [this message]
2018-05-08 15:30         ` Keith Busch
2018-05-10 20:52         ` Ming Lei
2018-05-10 20:52           ` Ming Lei
2018-05-10 21:05           ` Keith Busch
2018-05-10 21:05             ` Keith Busch
2018-05-10 21:10             ` Ming Lei
2018-05-10 21:10               ` Ming Lei
2018-05-10 21:18               ` Keith Busch
2018-05-10 21:18                 ` Keith Busch
2018-05-10 21:24                 ` Ming Lei
2018-05-10 21:24                   ` Ming Lei
2018-05-10 21:44                   ` Keith Busch
2018-05-10 21:44                     ` Keith Busch
2018-05-10 21:50                     ` Ming Lei
2018-05-10 21:50                       ` Ming Lei
2018-05-10 21:53                     ` Ming Lei
2018-05-10 21:53                       ` Ming Lei
2018-05-10 22:03                 ` Ming Lei
2018-05-10 22:03                   ` Ming Lei
2018-05-10 22:43                   ` Keith Busch
2018-05-10 22:43                     ` Keith Busch
2018-05-11  0:14                     ` Ming Lei
2018-05-11  0:14                       ` Ming Lei
2018-05-11  2:10             ` Ming Lei
2018-05-11  2:10               ` Ming Lei
2018-04-26 12:39 ` [PATCH 2/2] nvme: pci: guarantee EH can make progress Ming Lei
2018-04-26 12:39   ` Ming Lei
2018-04-26 16:24   ` Keith Busch
2018-04-26 16:24     ` Keith Busch
2018-04-28  3:28     ` Ming Lei
2018-04-28  3:28       ` Ming Lei

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