!14828 cgroup/cpuset: remove kernfs active break

	int retval = -ENODEV;

	buf = strstrip(buf);

	/*

	 * CPU or memory hotunplug may leave @cs w/o any execution

	 * resources, in which case the hotplug code asynchronously updates

	 * configuration and transfers all tasks to the nearest ancestor

	 * which can execute.

	 *

	 * As writes to "cpus" or "mems" may restore @cs's execution

	 * resources, wait for the previously scheduled operations before

	 * proceeding, so that we don't end up keep removing tasks added

	 * after execution capability is restored.

	 *

	 * cpuset_handle_hotplug may call back into cgroup core asynchronously

	 * via cgroup_transfer_tasks() and waiting for it from a cgroupfs

	 * operation like this one can lead to a deadlock through kernfs

	 * active_ref protection.  Let's break the protection.  Losing the

	 * protection is okay as we check whether @cs is online after

	 * grabbing cpuset_mutex anyway.  This only happens on the legacy

	 * hierarchies.

	 */

	css_get(&cs->css);

	kernfs_break_active_protection(of->kn);

	cpus_read_lock();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs))

out_unlock:

	mutex_unlock(&cpuset_mutex);

	cpus_read_unlock();

	kernfs_unbreak_active_protection(of->kn);

	css_put(&cs->css);

	flush_workqueue(cpuset_migrate_mm_wq);

	return retval ?: nbytes;

}