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From:   Roman Gushchin <guro@fb.com>
To:     Oleg Nesterov <oleg@redhat.com>
CC:     Roman Gushchin <guroan@gmail.com>, Tejun Heo <tj@kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v6 4/7] cgroup: cgroup v2 freezer
Thread-Topic: [PATCH v6 4/7] cgroup: cgroup v2 freezer
Thread-Index: AQHUmYm/FY3e3nKVvEu5zzs73euDdKXAH4WAgAU1PgCAAvBngIASo7UAgAToDoCAAAQjAA==
Date:   Thu, 14 Feb 2019 16:41:05 +0000
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On Thu, Feb 14, 2019 at 05:26:13PM +0100, Oleg Nesterov wrote:
> On 02/11, Roman Gushchin wrote:
> >
> > On Wed, Jan 30, 2019 at 05:52:01PM +0100, Oleg Nesterov wrote:
> > >
> > > Worse, this looks just wrong. In the latter case, cgroup becomes CGRP=
_FROZEN
> > > right after a 2nd task migrates to this cgroup, before this new task =
calls
> > > do_freezer_trap() or cgroup_enter_stopped().
> >
> > You're right. So, it looks like the problem is in the equation
> > nr_tasks_frozen + nr_tasks_stopped =3D=3D nr_tasks_to_freeze ,
> > because a task can be frozen and stopped simultaneously.
> >
> > So, basically it has to be
> > nr_tasks_frozen + nr_tasks_stopped >=3D nr_tasks_to_freeze instead.
>=20
> It seems you didn't read the paragraph above, or I missed something...
>=20
> How can "frozen + stopped >=3D to_freeze" fix the problem with the falsel=
y true
> CGRP_FROZEN ?

It helps with the problem when cgroup is mistakenly reported as non-frozen,
and adding a task makes it frozen due to increased nr_tasks_to_freeze.

But you're right, it's not correct. I have to think more how to make
the accounting work correctly with stopped tasks.

Roman