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Date:   Tue, 30 Apr 2019 11:41:50 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-acpi@...r.kernel.org,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH] ACPI / property: fix handling of data_nodes in
 acpi_get_next_subnode()

On 4/30/19 11:30 AM, Andy Shevchenko wrote:
> On Tue, Apr 30, 2019 at 10:52:29AM -0500, Pierre-Louis Bossart wrote:
>> When the DSDT tables expose devices with subdevices and a set of
>> hierarchical _DSD properties, the data returned by
>> acpi_get_next_subnode() is incorrect, with the results suggesting a bad
>> pointer assignment. The parser works fine with device_nodes or
>> data_nodes, but not with a combination of the two.
>>
>> The problem is traced to an invalid pointer used when jumping from
>> handling device_nodes to data nodes. The existing code looks for data
>> nodes below the last subdevice found instead of the common root. Fix
>> by forcing the acpi_device pointer to be derived from the same fwnode
>> for the two types of subnodes.
>>
>> This same problem of handling device and data nodes was already fixed
>> in a similar way by 'commit bf4703fdd166 ("ACPI / property: fix data
>> node parsing in acpi_get_next_subnode()")' but broken later by 'commit
>> 34055190b19 ("ACPI / property: Add fwnode_get_next_child_node()")', so
>> this should probably go to linux-stable all the way to 4.12
> 
> Period is missed in above sentence.
> 
> I think it make sense to add Fixes: tag.

Thanks Andy for the review. I hesitated to add a fixes tag. The line 
about resetting the adev pointer was indeed removed in the latter 
commit, but there were a slew of other changes done later by Sakari on 
hierarchical _DSD so it's quite complicated to say when this was last 
fully functional.

> 
> Nevertheless,
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> 
> Thank you for fixing this interesting issue!
> 
>>
>> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
>> ---
>>   drivers/acpi/property.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
>> index 5815356ea6ad..efc74f912f39 100644
>> --- a/drivers/acpi/property.c
>> +++ b/drivers/acpi/property.c
>> @@ -943,6 +943,16 @@ struct fwnode_handle *acpi_get_next_subnode(const struct fwnode_handle *fwnode,
>>   		const struct acpi_data_node *data = to_acpi_data_node(fwnode);
>>   		struct acpi_data_node *dn;
>>   
>> +		/*
>> +		 * We can have a combination of device and data nodes,
>> +		 * e.g. with hierarchical _DSD properties. Make sure
>> +		 * the adev pointer is restored before going through
>> +		 * data nodes, otherwise we will be looking for
>> +		 * data_nodes below the last device found instead of
>> +		 * the common fwnode shared by device_nodes and
>> +		 * data_nodes
>> +		 */
>> +		adev = to_acpi_device_node(fwnode);
>>   		if (adev)
>>   			head = &adev->data.subnodes;
>>   		else if (data)
>> -- 
>> 2.17.1
>>
> 

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