Re: [PATCH-next v3 1/3] cgroup/cpuset: Correctly set cpus_updated in cpuset_hotplug_update_tasks()

[Ridong Chen <ridong.chen@linux.dev>]

On 11/11/2026 10:02 AM, Waiman Long wrote:
> When cpuset_hotplug_update_tasks() is called with the conditions that
> remote_partition_disable() has to be called, the cs->effective_cpus will
> be updated such that it matches what is computed in new_cpus. In such
> case, cpus_updated can be incorrectly set to false leading to stale CPU
> afinity remained in the tasks not matching the new cpuset value. Fix that
> by forcing cpus_updated to true after calling remote_partition_disable().
> 
> Fixes: 181c8e091aae ("cgroup/cpuset: Introduce remote partition")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Link: https://sashiko.dev/#/bug/linux-ab90f7e8-0d60-40ca-83e9-e405075b24d2
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>   kernel/cgroup/cpuset.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 8a8a424a389f..862864b44960 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -4031,7 +4031,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>   {
>   	static cpumask_t new_cpus;
>   	static nodemask_t new_mems;
> -	bool cpus_updated;
> +	bool cpus_updated = false;
>   	bool mems_updated;
>   	int partcmd = -1;
>   	struct cpuset *parent;
> @@ -4044,12 +4044,17 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>   	if (!tmp || !cs->partition_root_state)
>   		goto update_tasks;
>   
> +	/*
> +	 * cpus_updated should be set to true when remote_partition_disable()
> +	 * is called as cs->effective_cpus will be modified.
> +	 */
>   	if (is_remote_partition(cs) && (cpumask_empty(subpartitions_cpus) ||
>   				       (cpumask_empty(&new_cpus) &&
>   					partition_is_populated(cs, NULL)))) {
>   		WRITE_ONCE(cs->prs_err, PERR_HOTPLUG);
>   		remote_partition_disable(cs, tmp);
>   		compute_effective_cpumask(&new_cpus, cs, parent);
> +		cpus_updated = true;
>   	}
>   
>   	/*
> @@ -4082,7 +4087,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
>   	}
>   
>   update_tasks:
> -	cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
> +	cpus_updated |= !cpumask_equal(&new_cpus, cs->effective_cpus);
>   	mems_updated = !nodes_equal(new_mems, cs->effective_mems);
>   	if (!cpus_updated && !mems_updated)
>   		goto unlock;	/* Hotplug doesn't affect this cpuset */

Reviewed-by: Ridong Chen <ridong.chen@linux.dev>
Thanks.

-- 
Best regards
Ridong