original.cc

int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags) {
  LIST_HEAD(tmp_links);
  struct cgroup *root_cgrp = &root->cgrp;
  struct kernfs_syscall_ops *kf_sops;
  struct css_set *cset;
  int i, ret;

  lockdep_assert_held(&cgroup_mutex);

  ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
  if (ret < 0)
    goto out;
  root_cgrp->id = ret;
  root_cgrp->ancestor_ids[0] = ret;

  ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, ref_flags,
                        GFP_KERNEL);
  if (ret)
    goto out;

  /*
   * We're accessing css_set_count without locking css_set_lock here,
   * but that's OK - it can only be increased by someone holding
   * cgroup_lock, and that's us.  Later rebinding may disable
   * controllers on the default hierarchy and thus create new csets,
   * which can't be more than the existing ones.  Allocate 2x.
   */
  ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
  if (ret)
    goto cancel_ref;

  ret = cgroup_init_root_id(root);
  if (ret)
    goto cancel_ref;

  kf_sops =
      root == &cgrp_dfl_root ? &cgroup_kf_syscall_ops : &cgroup1_kf_syscall_ops;

  root->kf_root = kernfs_create_root(
      kf_sops, KERNFS_ROOT_CREATE_DEACTIVATED | KERNFS_ROOT_SUPPORT_EXPORTOP,
      root_cgrp);
  if (IS_ERR(root->kf_root)) {
    ret = PTR_ERR(root->kf_root);
    goto exit_root_id;
  }
  root_cgrp->kn = root->kf_root->kn;

  ret = css_populate_dir(&root_cgrp->self);
  if (ret)
    goto destroy_root;

  ret = rebind_subsystems(root, ss_mask);
  if (ret)
    goto destroy_root;

  trace_cgroup_setup_root(root);

  /*
   * There must be no failure case after here, since rebinding takes
   * care of subsystems' refcounts, which are explicitly dropped in
   * the failure exit path.
   */
  list_add(&root->root_list, &cgroup_roots);
  cgroup_root_count++;

  /*
   * Link the root cgroup in this hierarchy into all the css_set
   * objects.
   */
  spin_lock_irq(&css_set_lock);
  hash_for_each(css_set_table, i, cset, hlist) {
    link_css_set(&tmp_links, cset, root_cgrp);
    if (css_set_populated(cset))
      cgroup_update_populated(root_cgrp, true);
  }
  spin_unlock_irq(&css_set_lock);

  BUG_ON(!list_empty(&root_cgrp->self.children));
  BUG_ON(atomic_read(&root->nr_cgrps) != 1);

  kernfs_activate(root_cgrp->kn);
  ret = 0;
  goto out;

destroy_root:
  kernfs_destroy_root(root->kf_root);
  root->kf_root = NULL;
exit_root_id:
  cgroup_exit_root_id(root);
cancel_ref:
  percpu_ref_exit(&root_cgrp->self.refcnt);
out:
  free_cgrp_cset_links(&tmp_links);
  return ret;
}