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/20181224091107.18354-1-mhocko@kernel.org
Fixes: 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the charge path")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Burt Holzman <burt@fnal.gov>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com
Cc: <stable@vger.kernel.org>	[4.19+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4afd5971f2d420f1c5b3099637dd4006bf193206..af7f18b32389e4ec0435128aa4b6d93fac6b80ca 100644 (file)
--- 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;
 }
 
 /**