linux-kernel - Re: [PATCH v6 4/7] cgroup: cgroup v2 freezer

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Message-ID: <20190214162612.GC19102@redhat.com>
Date:   Thu, 14 Feb 2019 17:26:13 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Roman Gushchin <guro@...com>
Cc:     Roman Gushchin <guroan@...il.com>, Tejun Heo <tj@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 4/7] cgroup: cgroup v2 freezer

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 == 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 >= nr_tasks_to_freeze instead.

It seems you didn't read the paragraph above, or I missed something...

How can "frozen + stopped >= to_freeze" fix the problem with the falsely true
CGRP_FROZEN ?

Oleg.