linux-kernel - [PATCH 3/3] gpio: use rcu_dereference

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Date: Tue, 13 Feb 2024 10:31:08 +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>,
	kernel test robot <oliver.sang@...el.com>
Subject: [PATCH 3/3] gpio: use rcu_dereference_protected() to make lockdep happy

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

Lockdep with CONFIG_PROVE_RCU enabled reports false positives about
suspicious rcu_dereference() usage. Let's silence it by using
rcu_dereference_protected().

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 | 12 ++++++++----
 drivers/gpio/gpiolib.h |  4 +++-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index c1391a9a0af6..d7503376b918 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -109,7 +109,8 @@ const char *gpiod_get_label(struct gpio_desc *desc)
 		return "interrupt";
 
 	return test_bit(FLAG_REQUESTED, &flags) ?
-			rcu_dereference(desc->label) : NULL;
+			rcu_dereference_protected(desc->label,
+					lockdep_is_held(&desc->srcu)) : NULL;
 }
 
 static int desc_set_label(struct gpio_desc *desc, const char *label)
@@ -2978,7 +2979,8 @@ static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
 
 	guard(srcu)(&gdev->srcu);
 
-	gc = rcu_dereference(gdev->chip);
+	gc = rcu_dereference_protected(gdev->chip,
+				       lockdep_is_held(&gdev->srcu));
 	if (!gc)
 		return -ENODEV;
 
@@ -3012,7 +3014,8 @@ static bool gpio_device_chip_cmp(struct gpio_device *gdev, struct gpio_chip *gc)
 {
 	guard(srcu)(&gdev->srcu);
 
-	return gc == rcu_dereference(gdev->chip);
+	return gc == rcu_dereference_protected(gdev->chip,
+					       lockdep_is_held(&gdev->srcu));
 }
 
 int gpiod_get_array_value_complex(bool raw, bool can_sleep,
@@ -3593,7 +3596,8 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 	gdev = desc->gdev;
 	/* FIXME Cannot use gpio_chip_guard due to const desc. */
 	guard(srcu)(&gdev->srcu);
-	gc = rcu_dereference(gdev->chip);
+	gc = rcu_dereference_protected(gdev->chip,
+				       lockdep_is_held(&gdev->srcu));
 	if (!gc)
 		return -ENODEV;
 
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 07443d26cbca..a857848b8955 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -14,6 +14,7 @@
 #include <linux/err.h>
 #include <linux/gpio/consumer.h> /* for enum gpiod_flags */
 #include <linux/gpio/driver.h>
+#include <linux/lockdep.h>
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/srcu.h>
@@ -202,7 +203,8 @@ DEFINE_CLASS(gpio_chip_guard,
 
 		_guard.gdev = desc->gdev;
 		_guard.idx = srcu_read_lock(&_guard.gdev->srcu);
-		_guard.gc = rcu_dereference(_guard.gdev->chip);
+		_guard.gc = rcu_dereference_protected(_guard.gdev->chip,
+					lockdep_is_held(&_guard.gdev->srcu));
 
 		_guard;
 	     }),
-- 
2.40.1