cgroup/cpuset: Enable update_tasks_cpumask() on top_cpuset

cgroup/cpuset: Enable update_tasks_cpumask() on top_cpuset

[ Upstream commit 957db468d3179eec33b609282aaace47b6d926ca ]

Previously, update_tasks_cpumask() is not supposed to be called with
top cpuset. With cpuset partition that takes CPUs away from the top
cpuset, adjusting the cpus_mask of the tasks in the top cpuset is
necessary. Percpu kthreads, however, are ignored.

Fixes: 1f6711b45834 ("cpuset: Add new v2 cpuset.sched.partition flag")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>