linux-kernel - [PATCH v2 3/4] gpio: use srcu_dereference() with SRCU-protected pointers

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Message-Id: <20240214084419.6194-4-brgl@bgdev.pl>
Date: Wed, 14 Feb 2024 09:44:18 +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 3/4] gpio: use srcu_dereference() with SRCU-protected pointers

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
srcu_dereference() which is the correct helper with SRCU.

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-sysfs.c |  5 +++--
 drivers/gpio/gpiolib.c       | 16 ++++++++--------
 drivers/gpio/gpiolib.h       |  3 ++-
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 6285fa5afbb1..71ba2a774197 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
+#include <linux/srcu.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
 
@@ -756,7 +757,7 @@ int gpiochip_sysfs_register(struct gpio_device *gdev)
 
 	guard(srcu)(&gdev->srcu);
 
-	chip = rcu_dereference(gdev->chip);
+	chip = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (!chip)
 		return -ENODEV;
 
@@ -800,7 +801,7 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 
 	guard(srcu)(&gdev->srcu);
 
-	chip = rcu_dereference(gdev->chip);
+	chip = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (chip)
 		return;
 
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 439d32d5aa38..b095f475805f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -109,7 +109,7 @@ const char *gpiod_get_label(struct gpio_desc *desc)
 		return "interrupt";
 
 	return test_bit(FLAG_REQUESTED, &flags) ?
-			rcu_dereference(desc->label) : NULL;
+			srcu_dereference(desc->label, &desc->srcu) : NULL;
 }
 
 static int desc_set_label(struct gpio_desc *desc, const char *label)
@@ -447,7 +447,7 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
 				 srcu_read_lock_held(&gpio_devices_srcu)) {
 		guard(srcu)(&gdev->srcu);
 
-		gc = rcu_dereference(gdev->chip);
+		gc = srcu_dereference(gdev->chip, &gdev->srcu);
 		if (!gc)
 			continue;
 
@@ -1190,7 +1190,7 @@ struct gpio_device *gpio_device_find(void *data,
 				 srcu_read_lock_held(&gpio_devices_srcu)) {
 		guard(srcu)(&gdev->srcu);
 
-		gc = rcu_dereference(gdev->chip);
+		gc = srcu_dereference(gdev->chip, &gdev->srcu);
 
 		if (gc && match(gc, data))
 			return gpio_device_get(gdev);
@@ -2978,7 +2978,7 @@ static int gpiod_get_raw_value_commit(const struct gpio_desc *desc)
 
 	guard(srcu)(&gdev->srcu);
 
-	gc = rcu_dereference(gdev->chip);
+	gc = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (!gc)
 		return -ENODEV;
 
@@ -3012,7 +3012,7 @@ 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 == srcu_dereference(gdev->chip, &gdev->srcu);
 }
 
 int gpiod_get_array_value_complex(bool raw, bool can_sleep,
@@ -3593,7 +3593,7 @@ 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 = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (!gc)
 		return -ENODEV;
 
@@ -4787,7 +4787,7 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_device *gdev)
 
 	guard(srcu)(&gdev->srcu);
 
-	gc = rcu_dereference(gdev->chip);
+	gc = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (!gc) {
 		seq_puts(s, "Underlying GPIO chip is gone\n");
 		return;
@@ -4872,7 +4872,7 @@ static int gpiolib_seq_show(struct seq_file *s, void *v)
 
 	guard(srcu)(&gdev->srcu);
 
-	gc = rcu_dereference(gdev->chip);
+	gc = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (!gc) {
 		seq_printf(s, "%s%s: (dangling chip)",
 			   priv->newline ? "\n" : "",
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 07443d26cbca..ada36aa0f81a 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -202,7 +202,8 @@ 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 = srcu_dereference(_guard.gdev->chip,
+					     &_guard.gdev->srcu);
 
 		_guard;
 	     }),
-- 
2.40.1