[BUGFIX][PATCH -stable] memcg: avoid oom-killing innocent task incase of use_hierarchy

[Daisuke Nishimura]

task_in_mem_cgroup(), which is called by select_bad_process() to check whether
a task can be a candidate for being oom-killed from memcg's limit, checks
"curr->use_hierarchy"("curr" is the mem_cgroup the task belongs to).

But this check return true(it's false positive) when:

	<some path>/00		use_hierarchy == 0	<- hitting limit
	  <some path>/00/aa	use_hierarchy == 1	<- "curr"

This leads to killing an innocent task in 00/aa. This patch is a fix for this
bug. And this patch also fixes the arg for mem_cgroup_print_oom_info(). We
should print information of mem_cgroup which the task being killed, not current,
belongs to.

Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
---
 mm/memcontrol.c |    2 +-
 mm/oom_kill.c   |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fd4529d..3acc226 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -496,7 +496,7 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
 	task_unlock(task);
 	if (!curr)
 		return 0;
-	if (curr->use_hierarchy)
+	if (mem->use_hierarchy)
 		ret = css_is_ancestor(&curr->css, &mem->css);
 	else
 		ret = (curr == mem);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a7b2460..ed452e9 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -400,7 +400,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 		cpuset_print_task_mems_allowed(current);
 		task_unlock(current);
 		dump_stack();
-		mem_cgroup_print_oom_info(mem, current);
+		mem_cgroup_print_oom_info(mem, p);
 		show_mem();
 		if (sysctl_oom_dump_tasks)
 			dump_tasks(mem);
-- 
1.5.6.1

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