From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH 3/3 cgroup/for-5.2-fixes] cgroup: Include dying leaders
 with live threads in PROCS iterations
Date: Fri, 10 Jan 2020 13:56:48 -0800
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To: Suren Baghdasaryan <surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny-IBi9RG/b67k@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Topi Miettinen <toiwoton-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, cgroups mailinglist <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, security-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org, Security Officers <security-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Lennart Poettering <lennart-mdGvqq1h2p+GdvJs77BJ7Q@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>, james.hsu-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, linger.lee-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, Tom Cherry <tomcherry-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>

Hello,

On Fri, Jan 10, 2020 at 01:47:19PM -0800, Suren Baghdasaryan wrote:
> So from user space's point of view the cgroup is empty and can be
> removed but rmdir() fails to do so. I think this behavior is
> inconsistent with the claim "cgroup which doesn't have any children
> and is associated only with zombie processes is considered empty and
> can be removed" from
> https://elixir.bootlin.com/linux/v5.4.10/source/Documentation/admin-guide/cgroup-v2.rst#L222

Yeah, the current behavior isn't quite consistent with the
documentation and what we prolly wanna do is allowing destroying a
cgroup with only dead processes in it.  That said, the correct (or at
least workable) signal which indicates that a cgroup is ready for
removal is cgroup.events::populated being zero, which is a poll(2)able
event.

Thanks.

-- 
tejun