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SubjectRe: [PATCH 1/4] cgroup: add CSS ID
Hi.

Sorry for very late reply.

It looks good in general.
Just a few comments.

> +/**
> + * css_lookup - lookup css by id
> + * @ss: cgroup subsys to be looked into.
> + * @id: the id
> + *
> + * Returns pointer to cgroup_subsys_state if there is valid one with id.
> + * NULL if not. Should be called under rcu_read_lock()
> + */
> +struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
> +{
> + struct css_id *cssid = NULL;
> +
> + BUG_ON(!ss->use_id);
> + cssid = idr_find(&ss->idr, id);
> +
> + if (unlikely(!cssid))
> + return NULL;
> +
> + return rcu_dereference(cssid->css);
> +}
> +
Just for clarification, is there any user of this function ?
(I agree it's natulal to define 'lookup' function, though.)

> +/**
> + * css_get_next - lookup next cgroup under specified hierarchy.
> + * @ss: pointer to subsystem
> + * @id: current position of iteration.
> + * @root: pointer to css. search tree under this.
> + * @foundid: position of found object.
> + *
> + * Search next css under the specified hierarchy of rootid. Calling under
> + * rcu_read_lock() is necessary. Returns NULL if it reaches the end.
> + */
> +struct cgroup_subsys_state *
> +css_get_next(struct cgroup_subsys *ss, int id,
> + struct cgroup_subsys_state *root, int *foundid)
> +{
> + struct cgroup_subsys_state *ret = NULL;
> + struct css_id *tmp;
> + int tmpid;
> + int rootid = css_id(root);
> + int depth = css_depth(root);
> +
I think it's safe here, but isn't it better to call css_id/css_depth
under rcu_read_lock(they call rcu_dereference) ?

> + if (!rootid)
> + return NULL;
> +
> + BUG_ON(!ss->use_id);
> + rcu_read_lock();
> + /* fill start point for scan */
> + tmpid = id;
> + while (1) {
> + /*
> + * scan next entry from bitmap(tree), tmpid is updated after
> + * idr_get_next().
> + */
> + spin_lock(&ss->id_lock);
> + tmp = idr_get_next(&ss->idr, &tmpid);
> + spin_unlock(&ss->id_lock);
> +
> + if (!tmp)
> + break;
> + if (tmp->depth >= depth && tmp->stack[depth] == rootid) {
Can't be css_is_ancestor used here ?
I think it would be more easy to understand.

> + ret = rcu_dereference(tmp->css);
> + if (ret) {
> + *foundid = tmpid;
> + break;
> + }
> + }
> + /* continue to scan from next id */
> + tmpid = tmpid + 1;
> + }
> +
> + rcu_read_unlock();
> + return ret;
> +}
> +


Thanks,
Daisuke Nishimura.


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