Re: [PATCH] platform/x86: thinkpad_acpi: Fix registration of tpacpi platform driver

["Kurt Borja" <kuurtb@gmail.com>]

Hi Mark,

On Sun Feb 9, 2025 at 7:54 PM -05, Mark Pearson wrote:
> Hi Kurt,
>
> On Sat, Feb 8, 2025, at 8:54 AM, Kurt Borja wrote:
>> On Sat Feb 8, 2025 at 11:26 AM -05, Mark Pearson wrote:
>>> Thanks Kurt,
>>>
>>> On Fri, Feb 7, 2025, at 11:56 PM, Kurt Borja wrote:
>>>> Hi Mark,
>>>>
>>>> On Sat Feb 8, 2025 at 4:14 AM -05, Mark Pearson wrote:
>>>>> When reviewing and testing the recent platform profile changes I had
>>>>> missed that they prevent the tpacpi platform driver from registering.
>>>>> This error is seen in the kernel logs, and the various tpacpi entries
>>>>> are not created:
>>>>> [ 7550.642171] platform thinkpad_acpi: Resources present before probing
>>>>
>>>> This happens because in thinkpad_acpi_module_init(), ibm_init() is
>>>> called before platform_driver_register(&tpacpi_pdriver), therefore
>>>> devm_platform_profile_register() is called before tpacpi_pdev probes.
>>>>
>>>> As you can verify in [1], in the probing sequence, the driver core
>>>> verifies the devres list is empty, which in this case is not because of
>>>> the devm_ call.
>>>>
>>>>>
>>>>> I believe this is because the platform_profile driver registers the
>>>>> device as part of it's initialisation in devm_platform_profile_register,
>>>>> and the thinkpad_acpi driver later fails as the resource is already used.
>>>>>
>>>>> Modified thinkpad_acpi so that it has a separate platform driver for the
>>>>> profile handling, leaving the existing tpacpi_pdev to register
>>>>> successfully.
>>>>
>>>> While this works, it does not address the problem directly. Also it is
>>>> discouraged to create "fake" platform devices [2].
>>>>
>>>> May I suggest moving tpacpi_pdriver registration before ibm_init()
>>>> instead, so ibm_init_struct's .init callbacks can use devres?
>>>>
>>>
>>> Yep - you're right. Moving it before the init does also fix it.
>>>
>>> I can't see any issues with this approach, but I'll test it out a bit more carefully and do an updated version with this approach.
>>
>> Thinking about it a bit more. With this approach you should maybe create
>> the tpacpi_pdev with platform_create_bundle() (I'm pretty sure you can
>> pass a NULL (*probe) callback) to avoid races.
>>
>> platform_create_bundle() only returns after the device has been
>> successfully bound to the driver.
>>
> Unfortunately having a null probe callback doesn't work - you end up with an oops for a null pointer dereference.

Are you sure? I just tested this on the for-next branch and it works
without issues. Also checked the code and (*probe) is only dereferenced
safely inside platform_bus_type's probe. Maybe another pointer is being
deferenced? Keep in mind that platform_create_bundle() also registers
the driver so maybe there is an issue there.

--
~ Kurt

>
> Thanks
> Mark