linux-kernel - [PATCH v2 4/4] gpio: don't let lockdep complain about inherently dangerous RCU usage

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Date: Wed, 14 Feb 2024 09:44:19 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>,
	Kent Gibson <warthog618@...il.com>,
	Alex Elder <elder@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Mark Brown <broonie@...nel.org>,
	Dan Carpenter <dan.carpenter@...aro.org>
Cc: linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	kernel test robot <oliver.sang@...el.com>
Subject: [PATCH v2 4/4] gpio: don't let lockdep complain about inherently dangerous RCU usage

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

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: d83cee3d2bb1 ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU")
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202402122234.d85cca9b-lkp@intel.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/gpio/gpiolib.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index b095f475805f..02be0ba1a402 100644
--- a/drivers/gpio/gpiolib.c
+++ b/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);
 
-- 
2.40.1