Commit c4c27fbd authored Apr 21, 2012 by Mike Galbraith Committed by Tejun Heo Apr 23, 2012

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>

parent 86f82d56

kernel/cgroup.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -60,6 +60,7 @@
		#include <linux/eventfd.h>
		#include <linux/poll.h>
		#include <linux/flex_array.h> /* used in cgroup_attach_proc */
		#include <linux/kthread.h>

		#include <linux/atomic.h>

		@@ -2225,6 +2226,18 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)

		if (threadgroup)
		tsk = tsk->group_leader;

		/*
		* Workqueue threads may acquire PF_THREAD_BOUND and become
		* trapped in a cpuset, or RT worker may be born in a cgroup
		* with no rt_runtime allocated. Just say no.
		*/
		if (tsk == kthreadd_task \|\| (tsk->flags & PF_THREAD_BOUND)) {
		ret = -EINVAL;
		rcu_read_unlock();
		goto out_unlock_cgroup;
		}

		get_task_struct(tsk);
		rcu_read_unlock();