Kernel panic via invalid cpuset domain rebuild

Denial of service in Linux allows local users to panic affected kernels by changing a cgroup v2 cpuset partition. update_parent_effective_cpumask accepts a non-null newmask without rechecking whether CPUs remain available to a parent cpuset containing tasks, then incorrectly rebuilds scheduling domains for an invalid partition root. Exploitation requires write access to cgroup v2 cpuset controls; success crashes or stalls the host rather than reading or modifying protected data.