linux-kernel - Re: [PATCH v10 3/9] cpuset: Simulate auto-off of sched.domain

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Message-ID: <20180620141144.GI2494@hirez.programming.kicks-ass.net>
Date:   Wed, 20 Jun 2018 16:11:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        Mike Galbraith <efault@....de>, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v10 3/9] cpuset: Simulate auto-off of sched.domain_root
 at cgroup removal

On Mon, Jun 18, 2018 at 12:14:02PM +0800, Waiman Long wrote:
> @@ -1058,7 +1060,12 @@ static int update_reserved_cpumask(struct cpuset *cpuset,
>  	 * Check if any CPUs in addmask or delmask are in the effective_cpus
>  	 * of a sibling cpuset. The implied cpu_exclusive of a scheduling
>  	 * domain root will ensure there are no overlap in cpus_allowed.
> +	 *
> +	 * This check is skipped if the cpuset is dying.

Comments that state what the code does are mostly useless; please
explain _why_ if anything.

>  	 */
> +	if (dying)
> +		goto updated_reserved_cpus;
> +
>  	rcu_read_lock();
>  	cpuset_for_each_child(sibling, pos_css, parent) {
>  		if ((sibling == cpuset) || !(sibling->css.flags & CSS_ONLINE))