memcg: check group leader fix

Remove unnecessary codes (...fragments of not-implemented
functionalilty...)

Reported-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2008,25 +2008,10 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
 				struct cgroup *old_cont,
 				struct task_struct *p)
 {
-	struct mm_struct *mm;
-	struct mem_cgroup *mem, *old_mem;
-
-	mm = get_task_mm(p);
-	if (mm == NULL)
-		return;
-
-	mem = mem_cgroup_from_cont(cont);
-	old_mem = mem_cgroup_from_cont(old_cont);
-
 	/*
-	 * Only thread group leaders are allowed to migrate, the mm_struct is
-	 * in effect owned by the leader
+	 * FIXME: It's better to move charges of this process from old
+	 * memcg to new memcg. But it's just on TODO-List now.
 	 */
-	if (!thread_group_leader(p))
-		goto out;
-
-out:
-	mmput(mm);
 }
 
 struct cgroup_subsys mem_cgroup_subsys = {