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Date: Mon, 8 Nov 2010 08:26:29 +0900
Message-ID: <AANLkTik4GfMEpE7HaXe93YSy-cTGKjDW1TgKYtOC2wos@mail.gmail.com>
Subject: Re: [patch 2/4] memcg: catch negative per-cpu sums in dirty info
From: Minchan Kim <minchan.kim@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Greg Thelen <gthelen@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Young <hidave.darkstar@gmail.com>,
        Andrea Righi <arighi@develer.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.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
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On Mon, Nov 8, 2010 at 7:14 AM, 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>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>


-- 
Kind regards,
Minchan Kim