[PATCH 16/23] gpiolib: cdev: Leverage revocable for lineevent_fileops

[Tzung-Bi Shih <tzungbi@kernel.org>]

Struct gpio_device now provides a revocable provider to the underlying
struct gpio_chip.  Leverage revocable for lineevent_fileops so that it
doesn't need to handle the synchronization by accessing the SRCU
explicitly.

Also, it's unneeded to hold a reference count to the struct gpio_device
while the file is opening.  The struct gpio_device
(i.e., (struct gpio_chip *)->gpiodev)) is valid as long as struct
gpio_chip is valid.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
 drivers/gpio/gpiolib-cdev.c | 46 ++++++++++++++++++++++++-------------
 1 file changed, 30 insertions(+), 16 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index f078d135a581..54150d718931 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -1772,7 +1772,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
 
 /**
  * struct lineevent_state - contains the state of a userspace event
- * @gdev: the GPIO device the event pertains to
+ * @chip_rev: revocable consumer handle for the corresponding struct gpio_chip
  * @label: consumer label used to tag descriptors
  * @desc: the GPIO descriptor held by this event
  * @eflags: the event flags this line was requested with
@@ -1785,7 +1785,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
  * event
  */
 struct lineevent_state {
-	struct gpio_device *gdev;
+	struct revocable *chip_rev;
 	const char *label;
 	struct gpio_desc *desc;
 	u32 eflags;
@@ -1805,10 +1805,10 @@ static __poll_t lineevent_poll(struct file *file,
 {
 	struct lineevent_state *le = file->private_data;
 	__poll_t events = 0;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&le->gdev->srcu);
-
-	if (!rcu_access_pointer(le->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(le->chip_rev, gc);
+	if (!gc)
 		return EPOLLHUP | EPOLLERR;
 
 	poll_wait(file, &le->wait, wait);
@@ -1843,10 +1843,10 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
 	ssize_t bytes_read = 0;
 	ssize_t ge_size;
 	int ret;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&le->gdev->srcu);
-
-	if (!rcu_access_pointer(le->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(le->chip_rev, gc);
+	if (!gc)
 		return -ENODEV;
 
 	/*
@@ -1901,15 +1901,24 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
 
 static void lineevent_free(struct lineevent_state *le)
 {
-	if (le->device_unregistered_nb.notifier_call)
-		blocking_notifier_chain_unregister(&le->gdev->device_notifier,
-						   &le->device_unregistered_nb);
+	if (le->device_unregistered_nb.notifier_call) {
+		struct gpio_chip *gc;
+
+		REVOCABLE_TRY_ACCESS_WITH(le->chip_rev, gc);
+		if (gc) {
+			struct gpio_device *gdev = gc->gpiodev;
+
+			blocking_notifier_chain_unregister(&gdev->device_notifier,
+					&le->device_unregistered_nb);
+		}
+	}
 	if (le->irq)
 		free_irq_label(free_irq(le->irq, le));
 	if (le->desc)
 		gpiod_free(le->desc);
 	kfree(le->label);
-	gpio_device_put(le->gdev);
+	if (le->chip_rev)
+		revocable_free(le->chip_rev);
 	kfree(le);
 }
 
@@ -1925,10 +1934,10 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
 	struct lineevent_state *le = file->private_data;
 	void __user *ip = (void __user *)arg;
 	struct gpiohandle_data ghd;
+	struct gpio_chip *gc;
 
-	guard(srcu)(&le->gdev->srcu);
-
-	if (!rcu_access_pointer(le->gdev->chip))
+	REVOCABLE_TRY_ACCESS_WITH(le->chip_rev, gc);
+	if (!gc)
 		return -ENODEV;
 
 	/*
@@ -2081,7 +2090,12 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
 	le = kzalloc(sizeof(*le), GFP_KERNEL);
 	if (!le)
 		return -ENOMEM;
-	le->gdev = gpio_device_get(gdev);
+
+	le->chip_rev = revocable_alloc(gdev->chip_rp);
+	if (!le->chip_rev) {
+		ret = -ENOMEM;
+		goto out_free_le;
+	}
 
 	if (eventreq.consumer_label[0] != '\0') {
 		/* label is only initialized if consumer_label is set */
-- 
2.52.0.457.g6b5491de43-goog