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From: Bart Van Assche <bart.vanassche@sandisk.com>
To: Ming Lei <tom.leiming@gmail.com>
Cc: Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>,
	Tejun Heo <tj@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Akinobu Mita <akinobu.mita@gmail.com>
Subject: Re: [PATCH 3/3] blk-mq: Fix the queue freezing mechanism
Date: Thu, 24 Sep 2015 09:43:48 -0700	[thread overview]
Message-ID: <56042844.60603@sandisk.com> (raw)
In-Reply-To: <20150924112251.2ec061fd@tom-T450>

On 09/23/2015 08:23 PM, Ming Lei wrote:
> IMO, mq_freeze_depth should only be accessed in slow path, and looks
> the race just happens during the small window between increasing
> 'mq_freeze_depth' and killing the percpu counter.

Hello Ming,

My concern is that *not* checking mq_freeze_depth in the hot path can 
cause a livelock. If there is a software layer, e.g. multipathd, that 
periodically submits new commands and if these commands take time to 
process e.g. because the transport layer is unavailable, how to 
guarantee that freezing ever succeeds without checking mq_freeze_depth 
in the hot path ?

Thanks,

Bart.

  reply	other threads:[~2015-09-24 16:43 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-23 22:11 [PATCH 0/3] Block layer patches for kernel v4.4 Bart Van Assche
2015-09-23 22:12 ` [PATCH 1/3] blk-cgroup: Declare local symbols static Bart Van Assche
2015-09-25 15:35   ` Tejun Heo
2015-09-23 22:12 ` [PATCH 2/3] bsg: Add sparse annotations to bsg_request_fn() Bart Van Assche
2015-09-23 22:14 ` [PATCH 3/3] blk-mq: Fix the queue freezing mechanism Bart Van Assche
2015-09-24  3:22   ` Ming Lei
2015-09-24 16:43     ` Bart Van Assche [this message]
2015-09-24 16:53       ` Tejun Heo
2015-09-24 17:35         ` Bart Van Assche
2015-09-24 17:49           ` Tejun Heo
2015-09-24 18:09             ` Bart Van Assche
2015-09-24 18:14               ` Tejun Heo
2015-09-24 22:54                 ` Bart Van Assche
2015-09-24 22:56                   ` Tejun Heo
2015-09-24 19:04     ` Bart Van Assche

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