[BUGFIX][PATCH] memcg: fix oom killing a child process in an othercgroup

[KAMEZAWA Hiroyuki]

This patch itself is againt mmotm-Feb10 but can be applied to 2.6.32.8
without problem.

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

Now, oom-killer is memcg aware and it finds the worst process from
processes under memcg(s) in oom. Then, it kills victim's child at first.
It may kill a child in other cgroup and may not be any help for recovery.
And it will break the assumption users have...

This patch fixes it.

CC: stable@xxxxxxxxxx
CC: Minchan Kim <minchan.kim@xxxxxxxxx>
CC: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
CC: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

---
 mm/oom_kill.c |    2 ++
 1 file changed, 2 insertions(+)

Index: mmotm-2.6.33-Feb10/mm/oom_kill.c
===================================================================
--- mmotm-2.6.33-Feb10.orig/mm/oom_kill.c
+++ mmotm-2.6.33-Feb10/mm/oom_kill.c
@@ -459,6 +459,8 @@ static int oom_kill_process(struct task_
 	list_for_each_entry(c, &p->children, sibling) {
 		if (c->mm == p->mm)
 			continue;
+		if (mem && !task_in_mem_cgroup(c, mem))
+			continue;
 		if (!oom_kill_task(c))
 			return 0;
 	}

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