Re: [PATCH v2 4/4] cpuset: generalize the validate_partition() interface

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

On 11/7/2026 11:59 AM, Waiman Long wrote:
> On 11/6/26 5:55 AM, Ridong Chen wrote:
>> From: Chen Ridong <chenridong@huawei.com>
>>
>> Refactor validate_partition() to take the parent partition, the new
>> partition root state, the new effective exclusive CPUs and the CPUs to
>> be deleted, instead of a trial cpuset. A NULL parent stands for a
>> remote partition, whose CPUs come from top_cpuset. This makes the
>> interface flexible enough to handle both local and remote partition
>> validation.
>>
>> The housekeeping conflict check is folded into validate_partition(). It
>> is skipped when the parent is not a valid partition root, as @cs can't
>> be a valid local partition in that case.
>>
>> Use the new interface for local partition enablement in
>> update_parent_effective_cpumask() and in partition_cpus_change(),
>> replacing the open-coded checks there. The order of the checks is now
>> the same for both paths: empty CPUs, housekeeping conflict, then no CPU
>> left for tasks.
>>
>> Signed-off-by: Chen Ridong <chenridong@huawei.com>
>> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
>> ---
>>   kernel/cgroup/cpuset.c | 112 +++++++++++++++++++----------------------
>>   1 file changed, 52 insertions(+), 60 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index a5ab9396eb61..1b0ac4e76ec7 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1434,6 +1434,41 @@ static bool prstate_housekeeping_conflict(int new_prs, 
>> int parent_prs,
>>       return res;
>>   }
>> +/**
>> + * validate_partition - Validate a cpuset partition configuration
>> + * @cs: The cpuset to validate
>> + * @parent: Parent partition of @cs, NULL for remote partition
>> + * @new_prs: The proposed new partition root state
>> + * @new_excpus: The new effective exclusive CPUs mask to validate
>> + * @del: exclusive CPUs to be deleted from @cs, can be NULL
>> + *
>> + * The housekeeping check is skipped if @parent is not a valid partition
>> + * root as @cs can't be a valid local partition in that case.
>> + *
>> + * Return: PRS error code (0 if valid, non-zero error code if invalid)
>> + */
>> +static enum prs_errcode validate_partition(struct cpuset *cs,
>> +        struct cpuset *parent, int new_prs,
>> +        struct cpumask *new_excpus, struct cpumask *del)
>> +{
>> +    int parent_prs = parent ? parent->partition_root_state : PRS_ROOT;
>> +
>> +    if (new_prs == PRS_MEMBER)
>> +        return PERR_NONE;
>> +
>> +    if (cpumask_empty(new_excpus))
>> +        return PERR_INVCPUS;
>> +
>> +    if ((parent_prs > 0) &&
>> +        prstate_housekeeping_conflict(new_prs, parent_prs, new_excpus, del))
>> +        return PERR_HKEEPING;
>> +
>> +    if (tasks_nocpu_error(parent_cs(cs), cs, new_excpus))
>> +        return PERR_NOCPUS;
> 
> For remote partition, the parent should be top_cpuset. I think we should set 
> parent to top_cpuset if NULL and pass it directly to tasks_nocpu_error().
> 

Good catch, thanks. parent_cs(cs) is wrong for a remote partition, since
its CPUs come from top_cpuset rather than its cgroup parent. I'll set
parent to &top_cpuset when it's NULL and pass it to tasks_nocpu_error():
	
	  if (!parent)
			  parent = &top_cpuset;
	  parent_prs = parent->partition_root_state;
	  if (parent_prs > 0 &&
		  prstate_housekeeping_conflict(new_prs, parent_prs, new_excpus, del))
			  return PERR_HKEEPING;
	
	  if (tasks_nocpu_error(parent, cs, new_excpus))
			  return PERR_NOCPUS;

> Other than that, the rests look good to me.
> 

Thanks for the review. Will fix it in v3.

-- 
Best regards
Ridong