linux-kernel - [PATCH v2 2/4] gpio: cdev: use correct pointer accessors with SRCU

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Message-Id: <20240214084419.6194-3-brgl@bgdev.pl>
Date: Wed, 14 Feb 2024 09:44:17 +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 2/4] gpio: cdev: use correct pointer accessors with SRCU

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

We never dereference the chip pointer in character device code so we can
use the lighter rcu_access_pointer() helper. This also makes lockep
happier as it no longer complains about suspicious rcu_dereference()
usage.

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>
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
---
 drivers/gpio/gpiolib-cdev.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 9323b357df43..85037fa4925e 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -206,7 +206,7 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd,
 
 	guard(srcu)(&lh->gdev->srcu);
 
-	if (!rcu_dereference(lh->gdev->chip))
+	if (!rcu_access_pointer(lh->gdev->chip))
 		return -ENODEV;
 
 	switch (cmd) {
@@ -1521,7 +1521,7 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
 
 	guard(srcu)(&lr->gdev->srcu);
 
-	if (!rcu_dereference(lr->gdev->chip))
+	if (!rcu_access_pointer(lr->gdev->chip))
 		return -ENODEV;
 
 	switch (cmd) {
@@ -1552,7 +1552,7 @@ static __poll_t linereq_poll(struct file *file,
 
 	guard(srcu)(&lr->gdev->srcu);
 
-	if (!rcu_dereference(lr->gdev->chip))
+	if (!rcu_access_pointer(lr->gdev->chip))
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &lr->wait, wait);
@@ -1574,7 +1574,7 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
 
 	guard(srcu)(&lr->gdev->srcu);
 
-	if (!rcu_dereference(lr->gdev->chip))
+	if (!rcu_access_pointer(lr->gdev->chip))
 		return -ENODEV;
 
 	if (count < sizeof(le))
@@ -1875,7 +1875,7 @@ static __poll_t lineevent_poll(struct file *file,
 
 	guard(srcu)(&le->gdev->srcu);
 
-	if (!rcu_dereference(le->gdev->chip))
+	if (!rcu_access_pointer(le->gdev->chip))
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &le->wait, wait);
@@ -1913,7 +1913,7 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
 
 	guard(srcu)(&le->gdev->srcu);
 
-	if (!rcu_dereference(le->gdev->chip))
+	if (!rcu_access_pointer(le->gdev->chip))
 		return -ENODEV;
 
 	/*
@@ -1996,7 +1996,7 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
 
 	guard(srcu)(&le->gdev->srcu);
 
-	if (!rcu_dereference(le->gdev->chip))
+	if (!rcu_access_pointer(le->gdev->chip))
 		return -ENODEV;
 
 	/*
@@ -2510,7 +2510,7 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	guard(srcu)(&gdev->srcu);
 
 	/* We fail any subsequent ioctl():s when the chip is gone */
-	if (!rcu_dereference(gdev->chip))
+	if (!rcu_access_pointer(gdev->chip))
 		return -ENODEV;
 
 	/* Fill in the struct and pass to userspace */
@@ -2595,7 +2595,7 @@ static __poll_t lineinfo_watch_poll(struct file *file,
 
 	guard(srcu)(&cdev->gdev->srcu);
 
-	if (!rcu_dereference(cdev->gdev->chip))
+	if (!rcu_access_pointer(cdev->gdev->chip))
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &cdev->wait, pollt);
@@ -2618,7 +2618,7 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
 
 	guard(srcu)(&cdev->gdev->srcu);
 
-	if (!rcu_dereference(cdev->gdev->chip))
+	if (!rcu_access_pointer(cdev->gdev->chip))
 		return -ENODEV;
 
 #ifndef CONFIG_GPIO_CDEV_V1
@@ -2696,7 +2696,7 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	guard(srcu)(&gdev->srcu);
 
 	/* Fail on open if the backing gpiochip is gone */
-	if (!rcu_dereference(gdev->chip))
+	if (!rcu_access_pointer(gdev->chip))
 		return -ENODEV;
 
 	cdev = kzalloc(sizeof(*cdev), GFP_KERNEL);
@@ -2796,8 +2796,7 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
 
 	guard(srcu)(&gdev->srcu);
 
-	gc = rcu_dereference(gdev->chip);
-	if (!gc)
+	if (!rcu_access_pointer(gdev->chip))
 		return -ENODEV;
 
 	chip_dbg(gc, "added GPIO chardev (%d:%d)\n", MAJOR(devt), gdev->id);
-- 
2.40.1