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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
Subject: Re: [patch 2/4] memcg: catch negative per-cpu sums in dirty info
Date: Mon, 8 Nov 2010 08:26:29 +0900	[thread overview]
Message-ID: <AANLkTik4GfMEpE7HaXe93YSy-cTGKjDW1TgKYtOC2wos@mail.gmail.com> (raw)
In-Reply-To: <20101107220353.414283590@cmpxchg.org>

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

  reply	other threads:[~2010-11-07 23:26 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-05 16:08 [PATCH] memcg: use do_div to divide s64 in 32 bit machine Minchan Kim
2010-11-05 16:34 ` Greg Thelen
2010-11-06  1:03 ` hannes
2010-11-06 17:19   ` Greg Thelen
2010-11-06 17:31     ` Minchan Kim
2010-11-07 22:14     ` [patch 0/4] memcg: variable type fixes Johannes Weiner
2010-11-07 22:14     ` [patch 1/4] memcg: use native word to represent dirtyable pages Johannes Weiner
2010-11-07 22:56       ` Minchan Kim
2010-11-08 22:25         ` Greg Thelen
2010-11-08 22:38           ` Johannes Weiner
2010-11-08 22:43             ` Greg Thelen
2010-11-16  3:37       ` KAMEZAWA Hiroyuki
2010-11-07 22:14     ` [patch 2/4] memcg: catch negative per-cpu sums in dirty info Johannes Weiner
2010-11-07 23:26       ` Minchan Kim [this message]
2010-11-08 22:28         ` Greg Thelen
2010-11-16  3:39       ` KAMEZAWA Hiroyuki
2010-11-07 22:14     ` [patch 3/4] memcg: break out event counters from other stats Johannes Weiner
2010-11-07 23:52       ` Minchan Kim
2010-11-08 23:20         ` Greg Thelen
2010-11-16  3:41       ` KAMEZAWA Hiroyuki
2010-11-07 22:14     ` [patch 4/4] memcg: use native word page statistics counters Johannes Weiner
2010-11-08  0:01       ` Minchan Kim
2010-11-08  9:08         ` Johannes Weiner
2010-11-08 22:51         ` Greg Thelen
2010-11-08  0:07       ` Minchan Kim
2010-11-08  9:37         ` memcg writeout throttling, was: " Johannes Weiner
2010-11-08 15:45           ` Wu Fengguang
2010-11-08 19:00             ` Greg Thelen
2010-11-08 23:27       ` Greg Thelen
2010-11-08 23:45         ` Johannes Weiner
2010-11-16  3:44       ` KAMEZAWA Hiroyuki

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