cgroup/cpuset: Don't allow creation of local partition over a remote one

[ Upstream commit 6da580ec ]

Currently, we don't allow the creation of a remote partition underneath
another local or remote partition. However, it is currently possible to
create a new local partition with an existing remote partition underneath
it if top_cpuset is the parent. However, the current cpuset code does
not set the effective exclusive CPUs correctly to account for those
that are taken by the remote partition.

Changing the code to properly account for those remote partition CPUs
under all possible circumstances can be complex. It is much easier to
not allow such a configuration which is not that useful. So forbid
that by making sure that exclusive_cpus mask doesn't overlap with
subpartitions_cpus and invalidate the partition if that happens.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>