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SubjectRe: patch] cpusets, cgroups: disallow attaching kthreadd
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On Tue, 2011-10-18 at 13:38 -0700, David Rientjes wrote:
> On Tue, 18 Oct 2011, Mike Galbraith wrote:
>
> > From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> >
> > cgroups: disallow attaching kthreadd
> >
> > Allowing kthreadd to be moved to a non-root group makes no sense, it being
> > a global resource, and needlessly leads unsuspecting users toward trouble.
> >
> > 1. An RT workqueue worker thread spawned in a task group with no rt_runtime
> > allocated is not schedulable. Simple user error, but harmful to the box.
> >
> > 2. A worker thread which acquires PF_THREAD_BOUND can never leave a cpuset,
> > rendering the cpuset immortal.
> >
>
> Eek, this seems like complete overkill, there may be cgroups now or in the
> future that it would be perfectly acceptable to move kthreadd into without
> any negative effects. There's no reason to restrict it this broadly,
> that's why I thought your change to cpusets was fine and acked it. It's
> the perfect candidate for what the ->can_attach() pointer for a cgroup can
> identify is problematic for _that_ cgroup.

Oh my, I can't win.

Either of the two patchlets will do the trick, so maintainer's choice.

> > Save the user some unexpected trouble, just say no.
> >
> > Signed-off-by: Mike Galbraith <efault@gmx.de>
> >
>
> A patch from Peter that only has your sign-off?

The only thing in it from me was a comment, figured I should post a from
line as a matter of propriety. Guess not. If this variant is the one
that flies, the from line can be dropped. I doubt Peter counts his
credits, and even if he did, he wouldn't notice _this one_ missing :)

-Mike



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