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 14:15:53 -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>

On Fri, Jan 10, 2020 at 02:14:19PM -0800, Suren Baghdasaryan wrote:
> > 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.
> 
> Unfortunately it would not be workable for us as it's only available
> for cgroup v2 controllers.
> I can think of other ways to fix it in the userspace but there might
> be other cgroup API users which are be broken after this change. I
> would prefer to fix it in the kernel if at all possible rather than
> chasing all possible users.

Yeah, the right thing to do is allowing destruction of cgroups w/ only
dead processes in it.

-- 
tejun