[PATCH] mm, memcg: fix inconsistent oom event behavior

[Yafang Shao <laoar.shao@gmail.com>]

A recent commit 9852ae3fe529 ("mm, memcg: consider subtrees in
memory.events") changes the behavior of memcg events, which will
consider subtrees in memory.events. But oom_kill event is a special one
as it is used in both cgroup1 and cgroup2. In cgroup1, it is displayed
in memory.oom_control. The file memory.oom_control is in both root memcg
and non root memcg, that is different with memory.event as it only in
non-root memcg. That commit is okay for cgroup2, but it is not okay for
cgroup1 as it will cause inconsistent behavior between root memcg and
non-root memcg.
Let's recover the original behavior for cgroup1.

Fixes: 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events")
Cc: Chris Down <chris@chrisdown.name>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/linux/memcontrol.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 8c340e6b347f..a0ae080a67d1 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -798,7 +798,8 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg,
 		atomic_long_inc(&memcg->memory_events[event]);
 		cgroup_file_notify(&memcg->events_file);
 
-		if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
+		if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS ||
+		    !cgroup_subsys_on_dfl(memory_cgrp_subsys))
 			break;
 	} while ((memcg = parent_mem_cgroup(memcg)) &&
 		 !mem_cgroup_is_root(memcg));
-- 
2.18.2