Re: [PATCH] ACPI: processor: Add acpi_processor_start() back to parse _CPC tables before CPU online

[zhenglifeng (A)]

Hi Pengjie,

On 8/26/2026 3:59 PM, Pengjie Zhang wrote:
> Hi Lifeng,
> 
> On 1/20/2026 7:32 PM, Lifeng Zheng wrote:
>> Currently, if boot with maxcpus less than NR_CPUS, the cppc_cpufreq driver
>> will fail to register. Because it requires the domain information of all
>> possible CPUs to construct shared_cpu_map, which shows the CPUs that share
>> the same domain.
>>
>> Commit c1385c1f0ba3 ("ACPI: processor: Simplify initial onlining to use
>> same path for cold and hotplug") removes probe() of acpi_processor_driver
>> and makes acpi_cppc_processor_probe() only being called the first time CPU
>> goes online. This means that CPUs that haven't yet gone online will not
>> have pre-parsed _CPC objects and causes cppc_cpufreq driver register fail.
>>
>> Add acpi_processor_start() back as the probe() callback of
>> acpi_processor_driver and call acpi_cppc_processor_probe() in it to make
>> sure all _CPC tables will be parsed when acpi_processor_driver registered.
>>
>> Fixes: c1385c1f0ba3 ("ACPI: processor: Simplify initial onlining to use same path for cold and hotplug")
>> Signed-off-by: Lifeng Zheng <zhenglifeng1@xxxxxxxxxx>
>> ---
>>   drivers/acpi/processor_driver.c | 30 ++++++++++++++++++++++++++----
>>   1 file changed, 26 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
>> index 65e779be64ff..c8b4daf580b0 100644
>> --- a/drivers/acpi/processor_driver.c
>> +++ b/drivers/acpi/processor_driver.c
>> @@ -33,6 +33,7 @@ MODULE_AUTHOR("Paul Diefenbaugh");
>>   MODULE_DESCRIPTION("ACPI Processor Driver");
>>   MODULE_LICENSE("GPL");
>>   +static int acpi_processor_start(struct device *dev);
>>   static int acpi_processor_stop(struct device *dev);
>>     static const struct acpi_device_id processor_device_ids[] = {
>> @@ -46,6 +47,7 @@ static struct device_driver acpi_processor_driver = {
>>       .name = "processor",
>>       .bus = &cpu_subsys,
>>       .acpi_match_table = processor_device_ids,
>> +    .probe = acpi_processor_start,
>>       .remove = acpi_processor_stop,
>>   };
>>   @@ -162,10 +164,6 @@ static int __acpi_processor_start(struct acpi_device *device)
>>       if (!pr)
>>           return -ENODEV;
>>   -    result = acpi_cppc_processor_probe(pr);
>> -    if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
>> -        dev_dbg(&device->dev, "CPPC data invalid or not present\n");
>> -
>>       if (!cpuidle_get_driver() || cpuidle_get_driver() == &acpi_idle_driver)
>>           acpi_processor_power_init(pr);
>>   @@ -192,6 +190,30 @@ static int __acpi_processor_start(struct acpi_device *device)
>>       return result;
>>   }
>>   +static int acpi_processor_start(struct device *dev)
>> +{
>> +    struct acpi_device *device = ACPI_COMPANION(dev);
>> +    struct acpi_processor *pr;
>> +    int result;
>> +
>> +    if (!device)
>> +        return -ENODEV;
>> +
>> +    pr = acpi_driver_data(device);
>> +    if (!pr)
>> +        return -ENODEV;
>> +
>> +    /* Protect against concurrent CPU hotplug operations */
>> +    cpu_hotplug_disable();
>> +    result = acpi_cppc_processor_probe(pr);
>> +    cpu_hotplug_enable();
>> +
>> +    if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
>> +        dev_dbg(&device->dev, "CPPC data invalid or not present\n");
>> +
>> +    return 0;
>> +}
>> +
>>   static int acpi_processor_stop(struct device *dev)
>>   {
>>       struct acpi_device *device = ACPI_COMPANION(dev);
> I reproduced the issue described by this patch on the latest kernel at
> commit 45c13f3f9e3bb15f.
> 
> On my system, CPU0 and CPU1 belong to the same software-coordinated
> frequency domain. After booting with maxcpus=1, CPU1 is present but
> offline, and its CPC descriptor is not parsed.
> 
> Consequently, acpi_get_psd_map() skips CPU1 and constructs an
> incomplete shared_cpu_map containing only CPU0.
> 
> When CPU1 is subsequently brought online:
> 
> echo 1 > /sys/devices/system/cpu/cpu1/online
> 
> the cpufreq core creates an overlapping policy and attempts to create
> the existing cpu0/cpufreq symbolic link again, resulting in the
> following warnings:
> ...
> sysfs_warn_dup
> sysfs_do_create_link_sd
> sysfs_create_link
> add_cpu_dev_symlink
> cpufreq_policy_online
> cpufreq_online
> cpuhp_cpufreq_online
> ...
> processor cpu0: cpufreq symlink creation failed
> 
> freq_qos_add_request() called for active request
> WARNING: kernel/power/qos.c:658 at freq_qos_add_request
> 
> The affected CPU masks are also inconsistent:
> 
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/affected_cpus
> 0
> 
> $ cat /sys/devices/system/cpu/cpu1/cpufreq/affected_cpus
> 0 1
> 
> After applying this patch on top of commit 45c13f3f9e3bb15f, the CPC
> descriptors are parsed before the CPUs are brought online. The
> shared_cpu_map is constructed correctly, and CPU1 can be brought
> online without triggering the duplicate sysfs link or active QoS
> request warnings.
> 
> This patch fixes the issue in my testing. so，
> 
> Tested-by: Pengjie Zhang <zhangpengjie2@xxxxxxxxxx>
> Reviewed-by: Pengjie Zhang <zhangpengjie2@xxxxxxxxxx>
> 

Thanks for the testing!