Re: [6.9 gpiolib regression] gpiolib: triggers: kobject: 'gpiochipX' is not, initialized, yet kobject_get() errors

[Andy Shevchenko <andy@kernel.org>]

On Tue, Apr 02, 2024 at 03:41:00PM +0200, Hans de Goede wrote:
> On 3/29/24 4:16 PM, Bartosz Golaszewski wrote:
> > On Fri, 29 Mar 2024 15:11:21 +0100, Hans de Goede <hans@hansg.org> said:

...

> > Thanks for the report. I hope I'm not being naive here but would the following
> > one-liner work?
> > 
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index ce94e37bcbee..69f365ccbfd8 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -1179,7 +1179,7 @@ struct gpio_device *gpio_device_find(const void *data,
> > 
> >  		gc = srcu_dereference(gdev->chip, &gdev->srcu);
> > 
> > -		if (gc && match(gc, data))
> > +		if (device_is_registered(&gdev->dev) && gc && match(gc, data))
> >  			return gpio_device_get(gdev);
> >  	}
> > 
> > This would make gpio_device_find() ignore any GPIO device that's not yet
> > registered on the GPIO bus which is almost the last step of the registration
> > process right before creating the sysfs attributes.
> 
> Yes that should work and it has the added advantage that it also waits
> for things like the irqchip to be setup before gpio_device_find() will
> find the gpio-device.
> 
> I cannot trigger the race every boot, but I do hit it quite regularly
> and with this change I've done 10 successful consecutive boots, so
> I believe that this indeed fixes the race.
> 
> I've prepared a patch with this fix now which I'll send out shortly.
> 
> As for Andy's suggestion I'm not all that familiar with the RCU stuff,
> but I think that if we were to go that route then the device_is_registered()
> check should be moved up to above the "guard(srcu)(&gdev->srcu);"
> line rather then above the "gc = srcu_deref..." line, since in that
> case we are not using the gdev->chip pointer at all if we bail ?

I believe you are right and we need to move this check out of SRCU scope.
(FWIW, I also thought the very same way after I had sent the message and
 was hesitating to reply with that.)

-- 
With Best Regards,
Andy Shevchenko