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SubjectRe: [patch] cpusets, cgroups: disallow attaching kthreadd
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On Tue, 2011-10-11 at 16:08 +0200, Peter Zijlstra wrote:
> On Mon, 2011-10-10 at 09:43 -0700, Tejun Heo wrote:
>
> > Yes, I think we need something like this. wq workers were using
> > PF_THREAD_BOUND to prevent diddling from userland which made some
> > unhappy.
>
> But that can be properly fixed.
>
> > Maybe we need a flag to properly indicate "don't diddle with
> > this thread from userland"? But, then, mainline kernel wouldn't need
> > the current PF_THREAD_BOUND at all. Peter, Steven, what do you think?
>
> Strict per-cpu affinity that is needed for correctness and disallows
> sched_setaffinity() is something entirely different from not being
> allowed to put something in a cgroup.

Agreed. The proposed patchlet is purely a practical matter.

> As to not allowing to put in a cgroup thing, is there anything other
> than kthreadd for which we need to enforce that? So far I've mostly
> treated it like: root can do stupid things, this is one of them, don't
> do that then.

Yeah, that's the other side of the coin. The only thing I can think of
justifying a response other than "well, gee, don't do that" is that Joe
User shouldn't need to know or care about kernel workqueue details.

I don't know of anything other than kthreadd where moving it here, or
over yonder matters one bit.

-Mike



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