code: def kill_all_tasks_recursively(self, kill_process_fn):
          
          def kill_all_tasks_in_cgroup_recursively(cgroup):
              files = [os.path.join(cgroup,f) for f in os.listdir(cgroup)]
              subdirs = filter(os.path.isdir, files)
  
              for subCgroup in subdirs:
                  kill_all_tasks_in_cgroup_recursively(subCgroup)
                  remove_cgroup(subCgroup)
  
              kill_all_tasks_in_cgroup(cgroup, kill_process_fn)
  
          for cgroup in self.paths:
              kill_all_tasks_in_cgroup_recursively(cgroup)
docs: Kill all tasks in this cgroup and all its children cgroups forcefully.
          Additionally, the children cgroups will be deleted.