gpio: take the SRCU read lock in gpiod_hog()

gpiod_hog() may be called without the gpio_device SRCU read lock taken
so we need to do it here as well. It's alright if someone else is
already holding the lock as SRCU read critical sections can be nested.

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]>
Reviewed-by: Linus Walleij <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>

Author: Bartosz Golaszewski

drivers/gpio/gpiolib.c

@@ -4492,24 +4492,27 @@ EXPORT_SYMBOL_GPL(gpiod_get_index_optional);
 int gpiod_hog(struct gpio_desc *desc, const char *name,
 	      unsigned long lflags, enum gpiod_flags dflags)
 {
-	struct gpio_chip *gc;
+	struct gpio_device *gdev = desc->gdev;
 	struct gpio_desc *local_desc;
 	int hwnum;
 	int ret;
 
+	CLASS(gpio_chip_guard, guard)(desc);
+	if (!guard.gc)
+		return -ENODEV;
+
 	if (test_and_set_bit(FLAG_IS_HOGGED, &desc->flags))
 		return 0;
 
-	gc = gpiod_to_chip(desc);
 	hwnum = gpio_chip_hwgpio(desc);
 
-	local_desc = gpiochip_request_own_desc(gc, hwnum, name,
+	local_desc = gpiochip_request_own_desc(guard.gc, hwnum, name,
 					       lflags, dflags);
 	if (IS_ERR(local_desc)) {
 		clear_bit(FLAG_IS_HOGGED, &desc->flags);
 		ret = PTR_ERR(local_desc);
 		pr_err("requesting hog GPIO %s (chip %s, offset %d) failed, %d\n",
-		       name, gc->label, hwnum, ret);
+		       name, gdev->label, hwnum, ret);
 		return ret;
 	}