On Tue, Sep 17, 2024 at 10:53:10AM +0200, Luca Ceresoli wrote:
> led-backlight is a consumer of one or multiple LED class devices, but no
> devlink is created for such supplier-producer relationship. One consequence
> is that removal ordered is not correctly enforced.
>
> Issues happen for example with the following sections in a device tree
> overlay:
>
> // An LED driver chip
> pca9632@62 {
> compatible = "nxp,pca9632";
> reg = <0x62>;
>
> // ...
>
> addon_led_pwm: led-pwm@3 {
> reg = <3>;
> label = "addon:led:pwm";
> };
> };
>
> backlight-addon {
> compatible = "led-backlight";
> leds = <&addon_led_pwm>;
> brightness-levels = <255>;
> default-brightness-level = <255>;
> };
>
> On removal of the above overlay, the LED driver can be removed before the
> backlight device, resulting in:
>
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
> ...
> Call trace:
> led_put+0xe0/0x140
> devm_led_release+0x6c/0x98
This looks like the object became invalid whilst we were holding a reference
to it. Is that reasonable? Put another way, is using devlink here fixing a
bug or merely hiding one?
Daniel.
