[33/39] memcg: avoid oom-killing innocent task in case of use_hierarchy

[Greg KH <gregkh@suse.de>]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------


From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

commit d31f56dbf8bafaacb0c617f9a6f137498d5c7aed upstream

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@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 mm/memcontrol.c |    8 +++++++-
 mm/oom_kill.c   |    2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -496,7 +496,13 @@ int task_in_mem_cgroup(struct task_struc
 	task_unlock(task);
 	if (!curr)
 		return 0;
-	if (curr->use_hierarchy)
+	/*
+	 * We should check use_hierarchy of "mem" not "curr". Because checking
+	 * use_hierarchy of "curr" here make this function true if hierarchy is
+	 * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
+	 * hierarchy(even if use_hierarchy is disabled in "mem").
+	 */
+	if (mem->use_hierarchy)
 		ret = css_is_ancestor(&curr->css, &mem->css);
 	else
 		ret = (curr == mem);
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -400,7 +400,7 @@ static int oom_kill_process(struct task_
 		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);