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Date: Tue, 17 Jan 2017 14:32:04 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>, Andy Lutomirski <luto@amacapital.net>,
        David Ahern <dsahern@gmail.com>,
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Subject: Re: Potential issues (security and otherwise) with the current
 cgroup-bpf API
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On Tue, Jan 17, 2017 at 02:03:03PM +0100, Michal Hocko wrote:
> On Sun 15-01-17 20:19:01, Tejun Heo wrote:
> [...]
> > So, what's proposed is a proper part of bpf.  In terms of
> > implementation, cgroup helps by hosting the pointers but that doesn't
> > necessarily affect the conceptual structure of it.  Given that, I
> > don't think it'd be a good idea to add anything to cgroup interface
> > for this feature.  Introspection is great to have but this should be
> > introspectable together with other bpf programs using the same
> > mechanism.  That's where it belongs.
> 
> If BPF only piggy backs on top of cgroup to iterate tasks shouldn't we
> at least enforce that the cgroup has to be a leaf one and no further
> children groups can be created once there is BPF program attached?

Why (again) this stupid constraint?

If you want to use cgroups for tagging (like perf does), _any_ parent
cgroup will also tag you.

So creating child cgroups, and placing tasks in it, should not be a
problem, the BPF thing should apply to all of them.