From: Li Zefan <lizf@cn.fujitsu.com>
Date: Thu, 15 Jan 2009 21:51:26 +0000 (-0800)
Subject: memcg: fix a race when setting memory.swappiness
X-Git-Tag: v2.6.29-rc2~17
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=068b38c1fa7a9210608f27ac521897ccc5f9b726;p=pandora-kernel.git

memcg: fix a race when setting memory.swappiness

(suppose: memcg->use_hierarchy == 0 and memcg->swappiness == 60)

echo 10 > /memcg/0/swappiness   |
  mem_cgroup_swappiness_write() |
    ...                         | echo 1 > /memcg/0/use_hierarchy
                                | mkdir /mnt/0/1
                                |   sub_memcg->swappiness = 60;
    memcg->swappiness = 10;     |

In the above scenario, we end up having 2 different swappiness
values in a single hierarchy.

We should hold cgroup_lock() when cheking cgrp->children list.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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