Re: [PATCH] gpio: gpiolib-of: Fix refcount bugs in of_mm_gpiochip_add_data()

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Mon, Jul 4, 2022 at 11:13 AM Liang He <windhl@xxxxxxx> wrote:
>
> We should use of_node_get() when a new reference of device_node
> is created. It is noted that the old reference stored in
> 'mm_gc->gc.of_node' should also be decreased.
>
> Fixes: f141ed65f256 ("gpio: Move DT support code into drivers/gpio")
> Signed-off-by: Liang He <windhl@xxxxxxx>
> ---
>  drivers/gpio/gpiolib-of.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> index 3d6c3ffd5576..de100b0217da 100644
> --- a/drivers/gpio/gpiolib-of.c
> +++ b/drivers/gpio/gpiolib-of.c
> @@ -860,7 +860,8 @@ int of_mm_gpiochip_add_data(struct device_node *np,
>         if (mm_gc->save_regs)
>                 mm_gc->save_regs(mm_gc);
>
> -       mm_gc->gc.of_node = np;
> +       of_node_put(mm_gc->gc.of_node);
> +       mm_gc->gc.of_node = of_node_get(np);
>
>         ret = gpiochip_add_data(gc, data);
>         if (ret)
> @@ -868,6 +869,7 @@ int of_mm_gpiochip_add_data(struct device_node *np,
>
>         return 0;
>  err2:
> +       of_node_put(np);
>         iounmap(mm_gc->regs);
>  err1:
>         kfree(gc->label);
> --
> 2.25.1
>

Have you noticed any issue with reference counting that made you post
this patch? We typically "borrow" the reference to the platform
device's of_node in GPIO drivers (and everywhere I can think of too).

Bart