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

[Yin Li]

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@xxxxxxxxxxxxxxxx>
>
> Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

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