Re: OOM notification for cgroupsv1 broken in 4.19

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, Dec 21, 2018 at 04:33:02PM +0100, Michal Hocko wrote:
> From 51633f683173013741f4d0ab3e31bae575341c55 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Fri, 21 Dec 2018 16:28:29 +0100
> Subject: [PATCH] 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.
> 
> Reported-by: Burt Holzman <burt@fnal.gov>
> Fixes: 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the charge path")
> Cc: stable # 4.19+
> Signed-off-by: Michal Hocko <mhocko@suse.com>

Looks good to me. The async side really does too much other stuff to
cleanly share code between them, so I don't mind separate code even if
it means they both have to do the mark, lock, notify dance.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>