Date: Tue, 16 Nov 2010 12:39:12 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Greg Thelen <gthelen@google.com>, Minchan Kim <minchan.kim@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Young <hidave.darkstar@gmail.com>,
        Andrea Righi <arighi@develer.com>,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Wu Fengguang <fengguang.wu@intel.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [patch 2/4] memcg: catch negative per-cpu sums in dirty info
Message-Id: <20101116123912.95d8605f.kamezawa.hiroyu@jp.fujitsu.com>
In-Reply-To: <20101107220353.414283590@cmpxchg.org>
References: <20101107215030.007259800@cmpxchg.org>
	<20101107220353.414283590@cmpxchg.org>
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On Sun,  7 Nov 2010 23:14:37 +0100
Johannes Weiner <hannes@cmpxchg.org> wrote:

> Folding the per-cpu counters can yield a negative value in case of
> accounting races between CPUs.
> 
> When collecting the dirty info, the code would read those sums into an
> unsigned variable and then check for it being negative, which can not
> work.
> 
> Instead, fold the counters into a signed local variable, make the
> check, and only then assign it.
> 
> This way, the function signals correctly when there are insane values
> instead of leaking them out to the caller.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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