memcg: use find_lock_task_mm() in memory cgroups oom

When the OOM killer scans task, it check a task is under memcg or
not when it's called via memcg's context.

But, as Oleg pointed out, a thread group leader may have NULL ->mm
and task_in_mem_cgroup() may do wrong decision. We have to use
find_lock_task_mm() in memcg as generic OOM-Killer does.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 8 insertions, 4 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ea5f5edf00b7..f52b0a1861c4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -47,6 +47,7 @@
 #include <linux/mm_inline.h>
 #include <linux/page_cgroup.h>
 #include <linux/cpu.h>
+#include <linux/oom.h>
 #include "internal.h"
 
 #include <asm/uaccess.h>
@@ -838,10 +839,13 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
 {
         int ret;
         struct mem_cgroup *curr = NULL;
+        struct task_struct *p;
 
-        task_lock(task);
-        curr = try_get_mem_cgroup_from_mm(task->mm);
-        task_unlock(task);
+        p = find_lock_task_mm(task);
+        if (!p)
+                return 0;
+        curr = try_get_mem_cgroup_from_mm(p->mm);
+        task_unlock(p);
         if (!curr)
                 return 0;
         /*
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d3def05a33d9..5014e50644d1 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -106,7 +106,7 @@ static void boost_dying_task_prio(struct task_struct *p,
  * pointer.  Return p, or any of its subthreads with a valid ->mm, with
  * task_lock() held.
  */
-static struct task_struct *find_lock_task_mm(struct task_struct *p)
+struct task_struct *find_lock_task_mm(struct task_struct *p)
 {
         struct task_struct *t = p;