linux-kernel - Re: [PATCH v8 0/7] freezer for cgroup v2

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Message-ID: <20190222163441.GA5596@redhat.com>
Date:   Fri, 22 Feb 2019 17:34:42 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Roman Gushchin <guro@...com>, Roman Gushchin <guroan@...il.com>,
        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 v8 0/7] freezer for cgroup v2

Hi,

On 02/21, Tejun Heo wrote:
>
> So, I really wanna avoid allowing userspace to cause D state sleeps.
...
> ptrace support is a lot less important than kill for sure but if at
> all possible I think it'd be better to have it

Tejun, I agree it would be better. I did not argue with that.

The question is how this can be implemented. And how much uglifications^W
complications in the core kernel code this needs.

> To summarize, the ideal result is the frozen state to be "stuck in
> jobctl stop loop"

Not sure I understand, but I don't think this can work...

Let me repeat, imo the freezer should be "reliable", it shouldn't stuck
in CGRP_FREEZE state forever if, say, it races with vfork(). And personally
I think this is more important than (very limited) ptrace support.

So I think it too should somehow interact with freezable_schedule/etc.

Oleg.