memcg: fix mem_cgroup_out_of_memory() return value.

mem_cgroup_out_of_memory() is returning "true" if it finds a TIF_MEMDIE
task after an eligible task was found, "false" if it found a TIF_MEMDIE
task before an eligible task is found.

This difference confuses memory_max_write() which checks the return
value of mem_cgroup_out_of_memory().  Since memory_max_write() wants to
continue looping, mem_cgroup_out_of_memory() should return "true" in
this case.

This patch sets a dummy pointer in order to return "true".

Link: http://lkml.kernel.org/r/1463753327-5170-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -1302,6 +1302,8 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 				mem_cgroup_iter_break(memcg, iter);
 				if (chosen)
 					put_task_struct(chosen);
+				/* Set a dummy value to return "true". */
+				chosen = (void *) 1;
 				goto unlock;
 			case OOM_SCAN_OK:
 				break;