Re: [PATCH v1 00/16] ACPI: Get rid of the list of children in struct acpi_device

Frank Rowand
2022-06-09T20:24:49Z

On 6/9/22 11:12, Andy Shevchenko wrote:
> On Thu, Jun 09, 2022 at 03:44:27PM +0200, Rafael J. Wysocki wrote:
>> Hi All,
>>
>> Confusingly enough, the ACPI subsystem stores the information on the given ACPI
>> device's children in two places: as the list of children in struct acpi_device
>> and (as a result of device registration) in the list of children in the embedded
>> struct device.
>>
>> These two lists agree with each other most of the time, but not always (like in
>> error paths in some cases), and the list of children in struct acpi_device is
>> not generally safe to use without locking. In principle, it should always be
>> walked under acpi_device_lock, but in practice holding acpi_scan_lock is
>> sufficient for that too. However, its users may not know whether or not
>> they operate under acpi_scan_lock and at least in some cases it is not accessed
>> in a safe way (note that ACPI devices may go away as a result of hot-remove,
>
>> unlike OF nodes).
>
> Hmm... Does it true for DT overlays? Not an expert in DT overlays, though,
> adding Rob and Frank.

DT nodes can be removed. The devicetree code uses devtree_lock and of_mutex
as needed for protection.

-Frank

>
>> For this reason, it is better to consolidate the code that needs to walk the
>> children of an ACPI device which is the purpose of this patch series.
>>
>> Overall, it switches over all of the users of the list of children in struct
>> acpi_device to using helpers based on the driver core's mechanics and finally
>> drops that list, but some extra cleanups are done on the way.
>>
>> Please refer to the patch changelogs for details.
>
> I'm going to look the individual patches.
>