From: Michal Hocko mhocko@suse.com

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.

Reported-by: Burt Holzman burt@fnal.gov Fixes: 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the charge path") Cc: stable # 4.19+ Acked-by: Johannes Weiner hannes@cmpxchg.org Signed-off-by: Michal Hocko mhocko@suse.com --- Hi Andrew, I forgot to CC you on the patch sent as a reply to the original bug report [1] so I am reposting with Ack from Johannes. Burt has confirmed this is resolving the regression for him [2]. 4.20 is out but I have marked the patch for stable so it should hit both 4.19 and 4.20.

[1] http://lkml.kernel.org/r/20181221153302.GB6410@dhcp22.suse.cz [2] http://lkml.kernel.org/r/96D4815C-420F-41B7-B1E9-A741E7523596@services.fnal....

mm/memcontrol.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6e1469b80cb7..7e6bf74ddb1e 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1666,6 +1666,9 @@ 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;

@@ -1700,10 +1703,23 @@ 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; }

/**