linux-kernel - Re: [PATCH v4 0/2] cgroup: allow management of subtrees by new cgroup namespaces

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Message-ID: <573F3B83.3020206@suse.de>
Date:	Sat, 21 May 2016 02:29:55 +1000
From:	Aleksa Sarai <asarai@...e.de>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Tejun Heo <tj@...nel.org>
Cc:	Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aleksa Sarai <cyphar@...har.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, dev@...ncontainers.org
Subject: Re: [PATCH v4 0/2] cgroup: allow management of subtrees by new cgroup
 namespaces

>>    This is stemming from the fact that an unpriv application can't
>> create its sub-cgroups without explicit delegation from the root and
>> that has always been an explicit design choice.
>> It's tied to who's responsible for cleanup afterwards and what
>> happens when the process gets migrated to a different cgroup.  The
>> latter is an important issue on v1 hierarchies because migrating
>> tasks sometimes is used as a way to control resource distribution.
>
> OK, so is the only problem cleanup?  If so, what if I proposed that a
> cgroup directory could only be created by the owner of the userns
> (which would be any old unprivileged user) iff they create a cgroup ns
> and the cgroup ns would be responsible for removing it again, so the
> cgroup subdirectory would be tied to the cgroup namespace as its holder
> and we'd use release of the cgroup to remove all the directories?

The only question I'd have is how would we deal with visibility (and 
should a "parent" cgroup namespace be able to modify things inside the 
cgroup?). And of course, how would that interact with VFS?

-- 
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/