linux-kernel - Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup in cpuset_init

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Date:   Wed, 27 Apr 2022 15:53:24 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Feng Tang <feng.tang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>, ying.huang@...el.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup
 in cpuset_init_smp()

Hello.

On Mon, Apr 25, 2022 at 11:55:05AM -0400, Waiman Long <longman@...hat.com> wrote:
> smp_init() is called after the first two init functions.  So we don't
> have a complete list of active cpus and memory nodes until later in
> cpuset_init_smp() which is the right time to set up effective_cpus
> and effective_mems.

Yes.

	setup_arch
	  prefill_possible_map
	cpuset_init (1)
	cgroup_init
	  cpuset_bind (2a)
	...
	kernel_init
	  kernel_init_freeable
	    ...
	      cpuset_init_smp (3)
	...
	...
	cpuset_bind (2b)


> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 9390bfd9f1cd..6bd8f5ef40fe 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -3390,8 +3390,9 @@ static struct notifier_block cpuset_track_online_nodes_nb = {
>   */
>  void __init cpuset_init_smp(void)
>  {
> -	cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
> -	top_cpuset.mems_allowed = node_states[N_MEMORY];
> +	/*
> +	 * cpus_allowd/mems_allowed will be properly set up in cpuset_bind().
> +	 */

IIUC, the comment should say

> +	 * cpus_allowed/mems_allowed were (v2) or will be (v1) properly set up in cpuset_bind().

(nit)

Reviewed-by: Michal Koutný <mkoutny@...e.com>