linux-kernel - Re: [patch 2/4] memcg: catch negative per-cpu sums in dirty info

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Date:	Mon, 8 Nov 2010 08:26:29 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Greg Thelen <gthelen@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <hidave.darkstar@...il.com>,
	Andrea Righi <arighi@...eler.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/4] memcg: catch negative per-cpu sums in dirty info

On Mon, Nov 8, 2010 at 7:14 AM, Johannes Weiner <hannes@...xchg.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@...xchg.org>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>


-- 
Kind regards,
Minchan Kim
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