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

[Andre Przywara <andre.przywara@arm.com>]

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>

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

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 {
>   		/*
>