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

[Michal Hocko]

From: Michal Hocko <mho...@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 <b...@fnal.gov>
Fixes: 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the charge path")
Cc: stable # 4.19+
Acked-by: Johannes Weiner <han...@cmpxchg.org>
Signed-off-by: Michal Hocko <mho...@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.gb6...@dhcp22.suse.cz
[2] 
http://lkml.kernel.org/r/96d4815c-420f-41b7-b1e9-a741e7523...@services.fnal.gov

 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;
 }
 
 /**
-- 
2.19.2