linux-kernel - Re: [PATCH v2 5/6] blk-mq: fix freeze queue race

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Message-ID: <20150709213747.GC18734@mtj.duckdns.org>
Date:	Thu, 9 Jul 2015 17:37:47 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v2 5/6] blk-mq: fix freeze queue race

On Thu, Jul 09, 2015 at 02:55:10PM +0800, Ming Lei wrote:
> This patch looks fine since at least changing DEAD state of percpu ref
> state should have been synchronized by caller.
> 
> Also looks __percpu_ref_switch_to_percpu() need to check if the refcount
> becomes dead after current switching, and seems something like following
> is needed:

Hmmm... but the caller is responsible for synchronization for these
operations.  If the state changes while waiting, it indicates a
synchronization bug and testing it one more time is kinda weird.  What
if it changes right after that test?

Thanks.

-- 
tejun
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