Re: [PATCH v5 5/5] cpuset: Rebuild root domain deadline accounting information

[Peter Zijlstra]

On Mon, Sep 03, 2018 at 04:28:01PM +0200, Juri Lelli wrote:
> +/*
> + * Called with cpuset_mutex held (rebuild_sched_domains())
> + * Called with hotplug lock held (rebuild_sched_domains_locked())
> + * Called with sched_domains_mutex held (partition_and_rebuild_domains())

Isn't that what we have lockdep_assert_held() for?

> + */
> +static void rebuild_root_domains(void)
> +{
> +	struct cpuset *cs = NULL;
> +	struct cgroup_subsys_state *pos_css;
> +
> +	rcu_read_lock();
> +
> +	/*
> +	 * Clear default root domain DL accounting, it will be computed again
> +	 * if a task belongs to it.
> +	 */
> +	dl_clear_root_domain(&def_root_domain);
> +
> +	cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
> +
> +		if (cpumask_empty(cs->effective_cpus)) {
> +			pos_css = css_rightmost_descendant(pos_css);
> +			continue;
> +		}
> +
> +		css_get(&cs->css);
> +
> +		rcu_read_unlock();

That looks really dodgy, but I suppose the comment near
css_next_descendant_pre() spells out that this is in fact OK.

> +		update_tasks_root_domain(cs);
> +
> +		rcu_read_lock();
> +		css_put(&cs->css);
> +	}
> +	rcu_read_unlock();
> +}