Re: [PATCH v1 1/4] hwmon: (acpi_power_meter) Fix using uninitialized variables

["lihuisong (C)" <lihuisong@huawei.com>]

在 2024/11/27 0:19, Guenter Roeck 写道:
> On 11/25/24 23:03, lihuisong (C) wrote:
>>
>> 在 2024/11/26 12:04, Guenter Roeck 写道:
>>> On 11/25/24 17:56, lihuisong (C) wrote:
>>>> Hi Guente,
>>>>
>>>> Thanks for your timely review.
>>>>
>>>> 在 2024/11/26 0:03, Guenter Roeck 写道:
>>>>> On 11/25/24 01:34, Huisong Li wrote:
>>>>>> The 'power1_alarm' attribute uses the 'power' and 'cap' in the
>>>>>> acpi_power_meter_resource structure. However, these two fields 
>>>>>> are just
>>>>>> updated when user query 'power' and 'cap' attribute, or hardware 
>>>>>> enforced
>>>>>> limit. If user directly query the 'power1_alarm' attribute 
>>>>>> without queryng
>>>>>> above two attributes, driver will use the uninitialized variables 
>>>>>> to judge.
>>>>>> In addition, the 'power1_alarm' attribute needs to update power 
>>>>>> and cap to
>>>>>> show the real state.
>>>>>>
>>>>>> Signed-off-by: Huisong Li <lihuisong@huawei.com>
>>>>>> ---
>>>>>>   drivers/hwmon/acpi_power_meter.c | 10 ++++++++++
>>>>>>   1 file changed, 10 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/hwmon/acpi_power_meter.c 
>>>>>> b/drivers/hwmon/acpi_power_meter.c
>>>>>> index 2f1c9d97ad21..4c3314e35d30 100644
>>>>>> --- a/drivers/hwmon/acpi_power_meter.c
>>>>>> +++ b/drivers/hwmon/acpi_power_meter.c
>>>>>> @@ -396,6 +396,9 @@ static ssize_t show_val(struct device *dev,
>>>>>>       struct acpi_device *acpi_dev = to_acpi_device(dev);
>>>>>>       struct acpi_power_meter_resource *resource = 
>>>>>> acpi_dev->driver_data;
>>>>>>       u64 val = 0;
>>>>>> +    int ret;
>>>>>> +
>>>>>> +    guard(mutex)(&resource->lock);
>>>>>>         switch (attr->index) {
>>>>>>       case 0:
>>>>>> @@ -423,6 +426,13 @@ static ssize_t show_val(struct device *dev,
>>>>>>               val = 0;
>>>>>>           break;
>>>>>>       case 6:
>>>>>> +        ret = update_meter(resource);
>>>>>> +        if (ret)
>>>>>> +            return ret;
>>>>>> +        ret = update_cap(resource);
>>>>>> +        if (ret)
>>>>>> +            return ret;
>>>>>> +
>>>>>>           if (resource->power > resource->cap)
>>>>>>               val = 1;
>>>>>>           else
>>>>>
>>>>>
>>>>> While technically correct, the implementation of this attribute 
>>>>> defeats its
>>>>> purpose. It is supposed to reflect the current status as reported 
>>>>> by the
>>>>> hardware. A real fix would be to use the associated notification 
>>>>> to set or
>>>>> reset a status flag, and to report the current value of that flag 
>>>>> as reported
>>>>> by the hardware.
>>>> I know what you mean.
>>>> The Notify(power_meter, 0x83) is supposed to meet your proposal IIUC.
>>>> It's good, but it depands on hardware support notification.
>>>>>
>>>>> If there is no notification support, the attribute should not even 
>>>>> exist,
>>>>> unless there is a means to retrieve its value from ACPI (the 
>>>>> status itself,
>>>>> not by comparing temperature values).
>>>> Currently, the 'power1_alarm' attribute is created just when 
>>>> platform support the power meter meassurement(bit0 of the supported 
>>>> capabilities in _PMC).
>>>> And it doesn't see if the platform support notifications.
>>>>  From the current implementation of this driver, this sysfs can 
>>>> also reflect the status by comparing power and cap,
>>>> which is good to the platform that support hardware limit from some 
>>>> out-of-band mechanism but doesn't support any notification.
>>>>
>>>
>>> The point is that this can also be done from userspace. Hardware 
>>> monitoring drivers
>>> are supposed to provide hardware attributes, not software attributes 
>>> derived from it.
>>>
>> So this 'power1_alarm' attribute can be exposed when platform 
>> supports hardware enforced limit and notifcations when the hardware 
>> limit is enforced, right?
>> If so, we have to change the condition that driver creates this sysfs 
>> interface.
>
> This isn't about enforcing anything, it is about reporting an alarm
> if the power consumed exceeds the maximum configured.
>
Sorry, I don't quite understand what you mean.
What your mean is to delete the current 'power1_alarm' sysfs and just 
use the related notify event to user?
How should we fix this issue?

/Huisong
>
> .