Re: [PATCH RFC 05/15] arm_mpam: Fix device_node refcount in DT resource parsing

[Yin Li <yin.li@oss.qualcomm.com>]

On 9/2/2026 9:29 PM, Andre Przywara wrote:
> Hi,
> 
> On 8/11/26 15:30, Yin Li wrote:
>> When a cache-parented or memory-controller-parented MSC is probed via
>> device tree, the parent node was assigned directly to a
>> __free(device_node) variable without incrementing its reference count.
>> Both the parent and the cache/memory variable are declared with
>> __free(device_node), which causes the compiler to automatically insert
>> an of_node_put() call for each variable when they go out of scope.
>> Since both variables point to the same node but the reference count was
>> only incremented once by of_get_parent(), the node ends up being
>> released twice, causing a refcount underflow.
> 
> Yes, looks about right: there is another assignment to both memory and 
> cache, they call of_parse_phandle(), which increments the refcount, so 
> we need to do the same for the direct assignments, to get the free'ing 
> done consistently.
> 
>> Use of_node_get() to take an explicit reference so each __free variable
>> holds its own reference.
>>
>> Signed-off-by: Yin Li <yin.li@oss.qualcomm.com>
> 
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> 

Hi Andre,

Thanks for the review and the Reviewed-by tag.

> ... though this should definitely be squashed into the respective DT 
> patches. Feel free to do so.
> 

You're right that these fixes should be squashed into the respective
DT patches. I kept them as separate fix patches for now because those
DT patches are based on James Morse's and Shanker's original unmerged
work — this way the changes I made on top are easier to review in
isolation. I plan to fold them back into the original patches once
James and Shanker have had a chance to respond.

> Cheers,
> Andre
> 
>> ---
>>   drivers/resctrl/mpam_devices.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/ 
>> mpam_devices.c
>> index 975ddab771b4..559fa09128b4 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -280,7 +280,7 @@ static int mpam_dt_parse_resource(struct mpam_msc 
>> *msc, struct device_node *np,
>>           type = MPAM_CLASS_CACHE;
>>       } else if (of_device_is_compatible(parent, "cache")) {
>> -        cache = parent;
>> +        cache = of_node_get(parent);
>>           type = MPAM_CLASS_CACHE;
>>       } else if (of_device_is_compatible(np, "arm,mpam-memory")) {
>>           memory = of_parse_phandle(np, "arm,mpam-device", 0);
>> @@ -290,7 +290,7 @@ static int mpam_dt_parse_resource(struct mpam_msc 
>> *msc, struct device_node *np,
>>           }
>>           type = MPAM_CLASS_MEMORY;
>>       } else if (of_device_is_compatible(np, "arm,mpam-memory- 
>> controller-msc")) {
>> -        memory = parent;
>> +        memory = of_node_get(parent);
>>           type = MPAM_CLASS_MEMORY;
>>       } else {
>>           /*
>>
> 

-- 
Thx and BRs,
Yin