weak.cc

void 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;

	lockdep_assert_held(&cgroup_mutex);

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

        percpu_ref_init(&root_cgrp->self.refcnt, css_release, ref_flags,
                        GFP_KERNEL);

	/*
	 * 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.
	 */
	allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);

	cgroup_init_root_id(root);

	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);
	root_cgrp->kn = root->kf_root->kn;

	css_populate_dir(&root_cgrp->self);

	rebind_subsystems(root, ss_mask);

	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);
}