On 2026/1/12 9:13, Chen Ridong wrote:
>
>
> On 2026/1/10 9:32, Waiman Long wrote:
>> Since commit f62a5d39368e ("cgroup/cpuset: Remove remote_partition_check()
>> & make update_cpumasks_hier() handle remote partition"), the
>> compute_effective_exclusive_cpumask() helper was extended to
>> strip exclusive CPUs from siblings when computing effective_xcpus
>> (cpuset.cpus.exclusive.effective). This helper was later renamed to
>> compute_excpus() in commit 86bbbd1f33ab ("cpuset: Refactor exclusive
>> CPU mask computation logic").
>>
>> This helper is supposed to be used consistently to compute
>> effective_xcpus. However, there is an exception within the callback
>> critical section in update_cpumasks_hier() when exclusive_cpus of a
>> valid partition root is empty. This can cause effective_xcpus value to
>> differ depending on where exactly it is last computed. Fix this by using
>> compute_excpus() in this case to give a consistent result.
>>
>> Signed-off-by: Waiman Long <[email protected]>
>> ---
>> kernel/cgroup/cpuset.c | 14 +++++---------
>> 1 file changed, 5 insertions(+), 9 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index da2b3b51630e..894131f47f78 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -2168,17 +2168,13 @@ static void update_cpumasks_hier(struct cpuset *cs,
>> struct tmpmasks *tmp,
>> spin_lock_irq(&callback_lock);
>> cpumask_copy(cp->effective_cpus, tmp->new_cpus);
>> cp->partition_root_state = new_prs;
>> - if (!cpumask_empty(cp->exclusive_cpus) && (cp != cs))
>> - compute_excpus(cp, cp->effective_xcpus);
>> -
>> /*
>> - * Make sure effective_xcpus is properly set for a valid
>> - * partition root.
>> + * Need to compute effective_xcpus if either exclusive_cpus
>> + * is non-empty or it is a valid partition root.
>> */
>> - if ((new_prs > 0) && cpumask_empty(cp->exclusive_cpus))
>> - cpumask_and(cp->effective_xcpus,
>> - cp->cpus_allowed, parent->effective_xcpus);
>> - else if (new_prs < 0)
>> + if ((new_prs > 0) || !cpumask_empty(cp->exclusive_cpus))
>> + compute_excpus(cp, cp->effective_xcpus);
>> + if (new_prs <= 0)
>> reset_partition_data(cp);
>> spin_unlock_irq(&callback_lock);
>>
>
> Looks good to me.
>
Reviewed-by: Chen Ridong <[email protected]>
--
Best regards,
Ridong
