linux-kernel - Re: [PATCH v12 8/8] cgroup: implement the PIDs subsystem

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Message-ID: <CAOviyaij2bays4aYQ_5HcopcBOfj4M_gKE7oQ_FsV38skK6vWA@mail.gmail.com>
Date:	Tue, 19 May 2015 18:44:39 +1000
From:	Aleksa Sarai <cyphar@...har.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tejun Heo <tj@...nel.org>, lizefan@...wei.com, mingo@...hat.com,
	richard@....at,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v12 8/8] cgroup: implement the PIDs subsystem

>> However, it should be noted that organisational operations (adding and
>> removing tasks from a PIDs hierarchy) will *not* be prevented.
>
> This is how you spell: broken controller.

This has been discussed before. Organisational operations (i.e.
attaching to a cgroup) are not to be blocked by a cgroup controller in
the unified hierarchy. You simply can't escape out of a parent
cgroup's limit through attaching to a child cgroup (because you will
attach either before the fork checks against the cgroup [in which case
the child's limit is followed -- which means you also follow the
parent's limit] or after it checks [which means you'll hit the
parent's limit and won't be able to fork]).

--
Aleksa Sarai (cyphar)
www.cyphar.com
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