Re: [PATCH 12/17] cgroup/cpuset: Invalidate children outside the new CPU mask

[Waiman Long <longman@redhat.com>]

On 8/20/26 8:41 AM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> When cpuset.cpus changes, compute_partition_effective_cpumask() builds a
> new exclusive mask but checks child partitions against
> cs->effective_xcpus. That field still contains the old mask, so a child
> that no longer fits can remain valid.
>
> Use new_xcpus for the check. A later partcmd_update() may revisit the
> newly invalid child. Report PERR_INVCPUS if the child CPUs are outside
> the parent effective exclusive mask so that this visit does not make the
> child valid again.
>
> Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2")
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>   kernel/cgroup/cpuset.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index b9faadf4af6d..b3e749ede7d1 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1987,12 +1987,16 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>   				adding = cpumask_and(tmp->addmask,
>   						     cs->effective_xcpus,
>   						     parent->effective_xcpus);
> -		} else if (is_partition_invalid(cs) && !cpumask_empty(xcpus) &&
> -			   cpumask_subset(xcpus, parent->effective_xcpus)) {
> +		} else if (is_partition_invalid(cs) && !cpumask_empty(xcpus)) {
>   			struct cgroup_subsys_state *css;
>   			struct cpuset *child;
>   			bool exclusive = true;
>   
> +			if (!cpumask_subset(xcpus, parent->effective_xcpus)) {
> +				part_error = PERR_INVCPUS;
> +				goto write_error;
> +			}
> +
A invalid partition means part_error should be set to some error code. 
This change only makes sure the error code is PERR_INVCPUS. Other than 
that, I don't see any other tangible change here.
>   			/*
>   			 * Convert invalid partition to valid has to
>   			 * pass the cpu exclusivity test.
> @@ -2144,7 +2148,7 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
>   		WARN_ON_ONCE(is_remote_partition(child));
>   		WRITE_ONCE(child->prs_err, 0);
>   		if (!cpumask_subset(child->effective_xcpus,
> -				    cs->effective_xcpus))
> +				    new_xcpus))
>   			WRITE_ONCE(child->prs_err, PERR_INVCPUS);
>   		else if (populated &&
>   			 cpumask_subset(new_ecpus, child->effective_xcpus))

This hunk should probably be grouped into the same patch making change 
to compute_partition_effective_cpumask().

Cheers,
Longman