linux-kernel - Re: [PATCH 1/3] md: set MD_CHANGE

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Message-ID: <20160508221227.GA2271@kernel.org>
Date:	Sun, 8 May 2016 15:12:27 -0700
From:	Shaohua Li <shli@...nel.org>
To:	Guoqing Jiang <gqjiang@...e.com>
Cc:	neilb@...e.de, linux-raid@...r.kernel.org,
	Martin Kepplinger <martink@...teo.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] md: set MD_CHANGE_PENDING in a atomic region

On Tue, May 03, 2016 at 10:22:13PM -0400, Guoqing Jiang wrote:
> Some code waits for a metadata update by:
> 
> 1. flagging that it is needed (MD_CHANGE_DEVS or MD_CHANGE_CLEAN)
> 2. setting MD_CHANGE_PENDING and waking the management thread
> 3. waiting for MD_CHANGE_PENDING to be cleared
> 
> If the first two are done without locking, the code in md_update_sb()
> which checks if it needs to repeat might test if an update is needed
> before step 1, then clear MD_CHANGE_PENDING after step 2, resulting
> in the wait returning early.
> 
> So make sure all places that set MD_CHANGE_PENDING are atomicial, and
> bit_clear_unless (suggested by Neil) is introduced for the purpose.

Applied the 3, thanks!