On Thu, Feb 05, 2026 at 05:57:15PM +0100, Bartosz Golaszewski wrote: > On Thu, Feb 5, 2026 at 9:52 AM Tzung-Bi Shih <[email protected]> wrote: > > > > On Wed, Feb 04, 2026 at 07:58:44AM -0500, Bartosz Golaszewski wrote: > > > On Tue, 3 Feb 2026 07:10:54 +0100, Tzung-Bi Shih <[email protected]> > > > said: > > > > diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h > > > > index 3abb90385829..cd136d5b52e9 100644 > > > > --- a/drivers/gpio/gpiolib.h > > > > +++ b/drivers/gpio/gpiolib.h > > > > @@ -52,6 +52,7 @@ > > > > * @device_notifier: used to notify character device wait queues about > > > > the GPIO > > > > * device being unregistered > > > > * @srcu: protects the pointer to the underlying GPIO chip > > > > + * @chip_rp: revocable provider handle for the corresponding struct > > > > gpio_chip. > > > > * @pin_ranges: range of pins served by the GPIO driver > > > > * > > > > * This state container holds most of the runtime variable data > > > > @@ -79,6 +80,7 @@ struct gpio_device { > > > > struct workqueue_struct *line_state_wq; > > > > struct blocking_notifier_head device_notifier; > > > > struct srcu_struct srcu; > > > > + struct revocable_provider __rcu *chip_rp; > > > > > > > > > > Why __rcu? This doesn't live in a different address space, only the > > > internal > > > resource it protects does. If anything - this could be > > > __attribute__((noderef)) > > > but even that is questionable as this is an opaque structure. > > > > For fixing a race on the pointer itself. See also [1]. > > > > [1] https://lore.kernel.org/all/[email protected] > > So we're just using a double RCU here? One to protect the resource and > another to protect the protector of the resource? I can't say I'm a > fan of this. I really want to like this interface but is there really > no way to hide the implementation details from the caller? Isn't this > the whole point? As it is: the user still has to care about an > RCU-protected pointer.
Will think about it but I have no better idea for now. Ideally, I think the user doesn't need to interact with the RCU (even if it's annotated with __rcu) but revocable APIs should handle it correctly.
