memcg: fix possible panic when CONFIG_MM_OWNER=y

When mm destruction happens, we should pass mm_update_next_owner() the old mm.
 But unfortunately new mm is passed in exec_mmap().

Thus, kernel panic is possible when a multi-threaded process uses exec().

Also, the owner member comment description is wrong.  mm->owner does not
necessarily point to the thread group leader.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: "Paul Menage" <menage@google.com>
Cc: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/exec.c b/fs/exec.c
index aeaa9791d8be..1f8a24aa1f8b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -736,7 +736,7 @@ static int exec_mmap(struct mm_struct *mm)
         tsk->active_mm = mm;
         activate_mm(active_mm, mm);
         task_unlock(tsk);
-        mm_update_next_owner(mm);
+        mm_update_next_owner(old_mm);
         arch_pick_mmap_layout(mm);
         if (old_mm) {
                 up_read(&old_mm->mmap_sem);