Re: [PATCH] cgroup/cpuset: prevent overlapping local and remote partition creation

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

On 9/20/2026 6:17 AM, Hui Peng wrote:
> Fix two partition validation bugs in kernel/cgroup/cpuset.c:
> 
> 1. In remote_partition_enable(), check whether the requested effective
>     xcpus intersect parent->subpartitions_cpus so a remote partition
>     cannot claim CPUs already delegated to a local child partition.
> 2. In validate_partition(), verify that enabling a local partition does
>     not overlap CPUs already allocated to an active remote partition.
> 
> Fixes: aa7d3a56a20f ("cpuset: fix warning when disabling remote partition")
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>

Could you please first describe what the issue is and how it can be triggered?
Or is there any reproducer?

> ---
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 2538faac9aba..13fad096c494 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -713,7 +713,10 @@ static inline bool cpus_excl_conflict(struct cpuset *trial, struct cpuset *sibli
>   		return true;
>   
>   	/* Exclusive_cpus cannot intersect */
> -	return cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus);
> +	return cpumask_intersects(trial->exclusive_cpus,
> +				  cpumask_empty(sibling->exclusive_cpus)
> +				  ? sibling->effective_xcpus
> +				  : sibling->exclusive_cpus);
>   }
>   
>   static inline bool mems_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
> @@ -1591,8 +1594,8 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   	 * above it or remote partition root underneath it is not allowed.
>   	 */
>   	compute_excpus(cs, tmp->new_cpus);
> -	WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
>   	if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
> +	    cpumask_intersects(tmp->new_cpus, subpartitions_cpus) ||
>   	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
>   		return PERR_INVCPUS;
>   	if (((new_prs == PRS_ISOLATED) &&
> @@ -2411,6 +2414,10 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri
>   	if (cpumask_empty(trialcs->effective_xcpus))
>   		return PERR_INVCPUS;
>   
> +	if ((parent == &top_cpuset) &&
> +	    cpumask_intersects(trialcs->effective_xcpus, subpartitions_cpus))
> +		return PERR_REMOTE;
> +
>   	if (prstate_housekeeping_conflict(trialcs->partition_root_state,
>   					  trialcs->effective_xcpus))
>   		return PERR_HKEEPING;
> @@ -2970,7 +2977,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
>   		 * local or remote partition.
>   		 */
>   		if ((parent == &top_cpuset) &&
> -		    cpumask_intersects(cs->exclusive_cpus, subpartitions_cpus)) {
> +		    cpumask_intersects(user_xcpus(cs), subpartitions_cpus)) {
>   			err = PERR_REMOTE;
>   			goto out;
>   		}

-- 
Best regards
Ridong