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

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Date:	Tue, 19 May 2015 23:43:21 +1000
From:	Aleksa Sarai <cyphar@...har.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>, 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
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]).
>
> That's complete and utter nonsense. What has the parent limit to do
> with the overflow of the child limit?
>
> parent:  limit 100   usecnt 80
> child:   limit 10    usecnt 10
>
> So moving anything into child is violating the constraints and has to
> be refused. Anything else is just dirty hackery.

Whoops. Yes, you're completely right. All right, I'll fix up the
patchset in a few days.

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