gpio: don't let lockdep complain about inherently dangerous RCU usage

There are two legacy, deprecated functions - gpiod_to_chip() and
gpio_device_get_chip() - that still have users in tree. They return the
address of the SRCU-protected chip outside of the read-only critical
sections. They are inherently dangerous and the users should convert to
safer alternatives. Let's explicitly silence lockdep warnings by using
rcu_dereference_check(ptr, 1). While at it: reuse
gpio_device_get_chip() in gpiod_to_chip().

Fixes: d83cee3 ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Signed-off-by: Bartosz Golaszewski <[email protected]>

Author: Bartosz Golaszewski

drivers/gpio/gpiolib.c

@@ -221,7 +221,8 @@ struct gpio_chip *gpiod_to_chip(const struct gpio_desc *desc)
 {
 	if (!desc)
 		return NULL;
-	return rcu_dereference(desc->gdev->chip);
+
+	return gpio_device_get_chip(desc->gdev);
 }
 EXPORT_SYMBOL_GPL(gpiod_to_chip);
 
@@ -291,7 +292,7 @@ EXPORT_SYMBOL(gpio_device_get_label);
  */
 struct gpio_chip *gpio_device_get_chip(struct gpio_device *gdev)
 {
-	return rcu_dereference(gdev->chip);
+	return rcu_dereference_check(gdev->chip, 1);
 }
 EXPORT_SYMBOL_GPL(gpio_device_get_chip);