From: Muchun Song <songmuchun@bytedance.com>
Date: Fri, 13 Nov 2020 22:52:13 -0800
Subject: mm: memcontrol: fix missing wakeup polling thread
Git-commit: 8b21ca0218d29cc6bb7028125c7e5a10dfb4730c
Patch-mainline: v5.10-rc4
References: bsc#1181584

When we poll the swap.events, we can miss being woken up when the swap
event occurs.  Because we didn't notify.

Fixes: f3a53a3a1e5b ("mm, memcontrol: implement memory.swap.events")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Yafang Shao <laoar.shao@gmail.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Tejun Heo <tj@kernel.org>
Link: https://lkml.kernel.org/r/20201105161936.98312-1-songmuchun@bytedance.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[mkoutny: Adjust for missing MEMCG_SWAP_HIGH]
Acked-by: Michal Koutný <mkoutny@suse.com>
---
 include/linux/memcontrol.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e391e3c56de56..a80c59af2c609 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -900,12 +900,18 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
 static inline void memcg_memory_event(struct mem_cgroup *memcg,
 				      enum memcg_memory_event event)
 {
+	bool swap_event = event == MEMCG_SWAP_MAX || event == MEMCG_SWAP_FAIL;
+
 	atomic_long_inc(&memcg->memory_events_local[event]);
-	cgroup_file_notify(&memcg->events_local_file);
+	if (!swap_event)
+		cgroup_file_notify(&memcg->events_local_file);
 
 	do {
 		atomic_long_inc(&memcg->memory_events[event]);
-		cgroup_file_notify(&memcg->events_file);
+		if (swap_event)
+			cgroup_file_notify(&memcg->swap_events_file);
+		else
+			cgroup_file_notify(&memcg->events_file);
 
 		if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
 			break;