cgroups: disallow attaching kthreadd or PF_THREAD_BOUND threads
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. Save the user some unexpected trouble, just say no. Signed-off-by: Mike Galbraith <mgalbraith@suse.de> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>
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