[BUGFIX][PATCH] memcg: use rcu_dereference to access mm->owner

[KAMEZAWA Hiroyuki]

the patch itself is against mmotm-Apr11.
Maybe it's better to apply 2.6.30-rc series.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

mm->owner should be accessed with rcu_dereference().

Reported-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 include/linux/memcontrol.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: mmotm-2.6.30-Apr11/include/linux/memcontrol.h
===================================================================
--- mmotm-2.6.30-Apr11.orig/include/linux/memcontrol.h
+++ mmotm-2.6.30-Apr11/include/linux/memcontrol.h
@@ -75,7 +75,7 @@ int mm_match_cgroup(const struct mm_stru
 {
 	struct mem_cgroup *mem;
 	rcu_read_lock();
-	mem = mem_cgroup_from_task((mm)->owner);
+	mem = mem_cgroup_from_task(rcu_dereference((mm)->owner));
 	rcu_read_unlock();
 	return cgroup == mem;
 }

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