Re: [PATCH -next RFC 05/16] cpuset: factor out partition_update() function

[Chen Ridong <chenridong@huaweicloud.com>]

On 2025/10/20 10:43, Waiman Long wrote:
> On 9/28/25 3:12 AM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@huawei.com>
>>
>> Extract the core partition update logic into a dedicated partition_update()
>> function. This refactoring centralizes updates to key cpuset data
>> structures including remote_sibling, effective_xcpus, partition_root_state,
>> and prs_err.
>>
>> The function handles the complete partition update workflow:
>> - Adding and removing exclusive CPUs via partition_xcpus_add()/del()
>> - Managing remote sibling relationships
>> - Synchronizing effective exclusive CPUs mask
>> - Updating partition state and error status
>> - Triggering required system updates and workqueue synchronization
>>
>> This creates a coherent interface for partition operations and establishes
>> a foundation for enhanced partition management while maintaining existing
>> remote partition behavior.
>>
>> Signed-off-by: Chen Ridong <chenridong@huawei.com>
>> ---
>>   kernel/cgroup/cpuset.c | 71 ++++++++++++++++++++++++++++--------------
>>   1 file changed, 47 insertions(+), 24 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 1944410ae872..0e2f95daf459 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1587,6 +1587,49 @@ static void partition_disable(struct cpuset *cs, struct cpuset *parent,
>>       cpuset_force_rebuild();
>>   }
>>   +/**
>> + * partition_update - Update an existing partition configuration
>> + * @cs: The cpuset to update
>> + * @prs: Partition root state (must be positive)
>> + * @xcpus: New exclusive CPUs mask for the partition (NULL to keep current)
>> + * @excpus: New effective exclusive CPUs mask
>> + * @tmp: Temporary masks
>> + *
>> + * Updates partition-related fields. The tmp->addmask is the CPU mask that
>> + * will be added to the subpartitions_cpus and removed from parent's
>> + * effective_cpus, and the tmp->delmask vice versa.
>> + */
>> +static void partition_update(struct cpuset *cs, int prs, struct cpumask *xcpus,
>> +                  struct cpumask *excpus, struct tmpmasks *tmp)
>> +{
>> +    bool isolcpus_updated;
>> +    bool excl_updated;
>> +    struct cpuset *parent;
>> +
>> +    lockdep_assert_held(&cpuset_mutex);
>> +    WARN_ON_ONCE(!cpuset_v2());
>> +    WARN_ON_ONCE(prs <= 0);
>> +
>> +    parent = is_remote_partition(cs) ? NULL : parent_cs(cs);
>> +    excl_updated = !cpumask_empty(tmp->addmask) ||
>> +            !cpumask_empty(tmp->delmask);
>> +
>> +    spin_lock_irq(&callback_lock);
>> +    isolcpus_updated = partition_xcpus_add(prs, parent, tmp->addmask);
>> +    isolcpus_updated |= partition_xcpus_del(prs, parent, tmp->delmask);
> 
> The current partition_xcpus_add/del() functions assume the given cpumas is non-empty. In the new
> partition_update() helper, you can pass an empty cpumask to them. This will cause useless work to be
> done. Also isolcpus_update may not be correct because of that causing unneeded work to be done in
> the workqueue code.
> 
> -Longman

Thank you, Longman.

I think we can add a check for empty cpumask inputs in partition_xcpus_add() and
partition_xcpus_del() to avoid unnecessary operations.

To clarify, do you mean that passing an empty cpumask to these functions might lead to incorrect
isolcpus_updated value? or are you referring to other potential logic issues?

-- 
Best regards,
Ridong