memcgroup: fix check for thread being a group leader in memcgroup

The check t->pid == t->pid is not the blessed way to check whether a task is a
group leader.

This is not about the code beautifulness only, but about pid namespaces fixes
- both the tgid and the pid fields on the task_struct are (slowly :( )
becoming deprecated.

Besides, the thread_group_leader() macro makes only one dereference :)

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.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/mm/memcontrol.c b/mm/memcontrol.c
index 8b9f6cae938e..9b648bd63451 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1079,7 +1079,7 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
          * Only thread group leaders are allowed to migrate, the mm_struct is
          * in effect owned by the leader
          */
-        if (p->tgid != p->pid)
+        if (!thread_group_leader(p))
                 goto out;
 
         css_get(&mem->css);