Re: [PATCH-next v2 3/6] cgroup/cpuset: Do housekeeping check before converting invalid partition to valid

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

On 10/11/2026 6:19 AM, Waiman Long wrote:
> When a hotplug event happens or when update_cpumasks_hier() is called, an
> invalid partition may be converted back to valid. However check against
> housekeeping conflict isn't being done which can lead to a partition
> state that violates the housekeeping rules. Update the code to allow
> reviving an invalid partition only if it can pass the housekeeping check.
> 
> Fixes: 4a74e418881f ("cgroup/cpuset: Check partition conflict with housekeeping setup")
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>   kernel/cgroup/cpuset.c | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 1c0441fa3bea..fb41cd76add6 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1374,6 +1374,13 @@ static bool prstate_housekeeping_conflict(int new_prs, int parent_prs,
>   	cpumask_var_t full_hk_cpus;
>   	int res;
>   
> +	/*
> +	 * For a currently invalid partition state, do the check assuming that
> +	 * it may be converted back to valid.
> +	 */
> +	if (new_prs < 0)
> +		new_prs = -new_prs;
> +

Personally, I don't like this. I think it should be certain what new_prs really 
is when prstate_housekeeping_conflict() is called; otherwise, it makes the code 
unreadable.

So I think when new_prs < 0, we should return false.

>   	if (housekeeping_enabled(HK_TYPE_DOMAIN_BOOT) && (new_prs == PRS_ROOT) &&
>   	    !cpumask_subset(add_cpus, housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT)))
>   		return true;
> @@ -1956,9 +1963,16 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>   			bool exclusive = true;
>   
>   			/*
> -			 * Convert invalid partition to valid has to
> -			 * pass the cpu exclusivity test.
> +			 * Convert invalid partition to valid has to pass the
> +			 * cpu exclusivity test as well as the housekeeping
> +			 * check.
>   			 */
> +			if (prstate_housekeeping_conflict(cs->partition_root_state,
> +							  parent->partition_root_state,
> +							  xcpus, NULL)) {
> +				part_error = PERR_HKEEPING;
> +				goto write_error;
> +			}
>   			rcu_read_lock();
>   			cpuset_for_each_child(child, css, parent) {
>   				if (child == cs)

-- 
Best regards
Ridong