linux-kernel - [PATCH v2 02/23] gpio: of: assign and read the hog pointer atomically

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Date: Mon,  5 Feb 2024 10:33:57 +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>
Cc: linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH v2 02/23] gpio: of: assign and read the hog pointer atomically

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

The device nodes representing GPIO hogs cannot be deleted without
unregistering the GPIO chip so there's no need to serialize their access.
However we must ensure that users can get the right address so write and
read it atomically.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
---
 drivers/gpio/gpiolib-of.c | 4 ++--
 drivers/gpio/gpiolib.c    | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index 77509aa19900..bd6b8702c790 100644
--- a/drivers/gpio/gpiolib-of.c
+++ b/drivers/gpio/gpiolib-of.c
@@ -800,7 +800,7 @@ static int of_gpiochip_add_hog(struct gpio_chip *chip, struct device_node *hog)
 			return ret;
 
 #ifdef CONFIG_OF_DYNAMIC
-		desc->hog = hog;
+		WRITE_ONCE(desc->hog, hog);
 #endif
 	}
 
@@ -848,7 +848,7 @@ static void of_gpiochip_remove_hog(struct gpio_chip *chip,
 	struct gpio_desc *desc;
 
 	for_each_gpio_desc_with_flag(chip, desc, FLAG_IS_HOGGED)
-		if (desc->hog == hog)
+		if (READ_ONCE(desc->hog) == hog)
 			gpiochip_free_own_desc(desc);
 }
 
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index a14eef93ead8..4c18b693d06c 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2324,7 +2324,7 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
 		clear_bit(FLAG_EDGE_FALLING, &desc->flags);
 		clear_bit(FLAG_IS_HOGGED, &desc->flags);
 #ifdef CONFIG_OF_DYNAMIC
-		desc->hog = NULL;
+		WRITE_ONCE(desc->hog, NULL);
 #endif
 		ret = true;
 	}
-- 
2.40.1