memcg, oom: notify on oom killer invocation from the charge path

Burt Holzman has noticed that memcg v1 doesn't notify about OOM events via
eventfd anymore.  The reason is that 29ef680ae7c2 ("memcg, oom: move
out_of_memory back to the charge path") has moved the oom handling back to
the charge path.  While doing so the notification was left behind in
mem_cgroup_oom_synchronize.

Fix the issue by replicating the oom hierarchy locking and the
notification.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the charge path")
Signed-off-by: Michal Hocko <[email protected]>
Reported-by: Burt Holzman <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Vladimir Davydov <[email protected]
Cc: <[email protected]>	[4.19+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 18 insertions, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4afd5971f2d4..af7f18b32389 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1673,6 +1673,9 @@ enum oom_status {
 
 static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
 {
+	enum oom_status ret;
+	bool locked;
+
 	if (order > PAGE_ALLOC_COSTLY_ORDER)
 		return OOM_SKIPPED;
 
@@ -1707,10 +1710,23 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int
 		return OOM_ASYNC;
 	}
 
+	mem_cgroup_mark_under_oom(memcg);
+
+	locked = mem_cgroup_oom_trylock(memcg);
+
+	if (locked)
+		mem_cgroup_oom_notify(memcg);
+
+	mem_cgroup_unmark_under_oom(memcg);
 	if (mem_cgroup_out_of_memory(memcg, mask, order))
-		return OOM_SUCCESS;
+		ret = OOM_SUCCESS;
+	else
+		ret = OOM_FAILED;
 
-	return OOM_FAILED;
+	if (locked)
+		mem_cgroup_oom_unlock(memcg);
+
+	return ret;
 }
 
 /**