cgroup/cpuset: Fix wrong check in update_parent_subparts_cpumask()

In the Linux kernel, the following vulnerability has been resolved:

cgroup/cpuset: Fix wrong check in update_parent_subparts_cpumask()

It was found that the check to see if a partition could use up all

the cpus from the parent cpuset in update_parent_subparts_cpumask()

was incorrect. As a result, it is possible to leave parent with no

effective cpu left even if there are tasks in the parent cpuset. This

can lead to system panic as reported in [1].

Fix this probem by updating the check to fail the enabling the partition

if parent's effective_cpus is a subset of the child's cpus_allowed.

Also record the error code when an error happens in update_prstate()

and add a test case where parent partition and child have the same cpu

list and parent has task. Enabling partition in the child will fail in

this case.

[1] https://www.spinics.net/lists/cgroups/msg36254.html