[$] A "kill" button for control groups

The kernel's control-group mechanism existsto partition processes and to provide resource guarantees (and limits) for each. Processes runningwithin a properly configured control group are unable to deprivethose running in a different group of their allocated resources (CPU time,memory, I/O bandwidth, etc.), and are equally protected from interferenceby others. With few exceptions, control groups are not used to takedirect actions on processes; Christian Brauner's cgroup.killpatch set is meant to be one of those exceptions.