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SubjectRe: [patch] cpusets, cgroups: disallow attaching kthreadd
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.

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.

I don't think its horribly bad to change the affinity mask of kthreadd,
if a sibling kthread needs a specific affinity it should set that and
override whatever it inherits. If it runs with the default, its a neat
way of setting that.

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