Re: [PATCH v1 3/3] cgroup: relax common ancestor restriction for direct descendants

From: Tejun Heo
Date: Wed Jul 20 2016 - 11:51:59 EST

Hello, Aleksa.

On Tue, Jul 19, 2016 at 02:18:16AM +1000, Aleksa Sarai wrote:
> If we're moving from a parent to a direct descendant, the only end
> result (on cgroupv2 hierarchies) is that the process experiences more
> restrictive resource limits. Thus, there's no reason to restrict
> processes from moving to direct descendants based on whether or not they
> have cgroup.procs write access to their current cgroup.
> This is important for unprivileged subtree management, as it allows
> unprivileged processes to move to their newly create subtrees.

I don't think we can do this as this allows a sub-cgroup to steal an
ancestor's process whether the ancestor likes it or not. A process
being put in a context where it's more restricted without whatever is
managing that part of cgroup hierarchy is not ok, at all. Please also
note that nobody expects its processes to be stolen underneath it.
This would be a management nightmare.