memcg: avoid oom-killing innocent task in case of use_hierarchy

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>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fd4529d86de59cbfc7093a433752e9b9b604dc93..566925e7cdbda7bfc8631554e070f6b798325d59 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -496,7 +496,13 @@ 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)
+       /*
+        * 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);

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a7b2460e922b779252ebcc225cecaf6060b0e964..ed452e9485d4cb6ddcd16b23b34561ad59c052d7 100644 (file)
--- 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);