static void cgroup_kill_sb(struct super_block *sb)
{
	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
	struct cgroup_root *root = cgroup_root_from_kf(kf_root);

	/*
	 * If @root doesn't have any children, start killing it.
	 * This prevents new mounts by disabling percpu_ref_tryget_live().
	 *
	 * And don't kill the default root.
	 */
	if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
	    !percpu_ref_is_dying(&root->cgrp.self.refcnt)) {
		cgroup_bpf_offline(&root->cgrp);
		percpu_ref_kill(&root->cgrp.self.refcnt);
	}
	cgroup_put(&root->cgrp);
	kernfs_kill_sb(sb);
}
static void cgroup_kill_sb(struct super_block *sb)
{
	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
	struct cgroup_root *root = cgroup_root_from_kf(kf_root);

	 
	if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
	    !percpu_ref_is_dying(&root->cgrp.self.refcnt)) {
		cgroup_bpf_offline(&root->cgrp);
		percpu_ref_kill(&root->cgrp.self.refcnt);
	}
	cgroup_put(&root->cgrp);
	kernfs_kill_sb(sb);
}