Hello Daniel,
On Thu, 19 Sep 2024 14:43:23 +0200
Daniel Thompson <daniel.thompson@xxxxxxxxxx> wrote:
> 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?
Thanks for your comment.
Hervé and I just had a look at the code and there actually might be a
bug here, which we will be investigating (probably next week).
Still I think the devlink needs to be added to describe the
relationship between the supplier (LED) and consumer (backlight).
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
