linux-kernel - [PATCH v2 4/6] gpio: cdev: wake up chardev poll() on device unbind

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Message-Id: <20230817184958.25349-5-brgl@bgdev.pl>
Date:   Thu, 17 Aug 2023 20:49:56 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kent Gibson <warthog618@...il.com>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH v2 4/6] gpio: cdev: wake up chardev poll() on device unbind

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

Add a notifier block to the gpio_chardev_data structure and register it
with the gpio_device's device notifier. Upon reception of an event, wake
up the wait queue so that the user-space be forced out of poll() and need
to go into a new system call which will then fail due to the chip being
gone.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/gpio/gpiolib-cdev.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index f95e1b110311..8b081c9b8d27 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2320,6 +2320,7 @@ struct gpio_chardev_data {
 	wait_queue_head_t wait;
 	DECLARE_KFIFO(events, struct gpio_v2_line_info_changed, 32);
 	struct notifier_block lineinfo_changed_nb;
+	struct notifier_block device_unregistered_nb;
 	unsigned long *watched_lines;
 #ifdef CONFIG_GPIO_CDEV_V1
 	atomic_t watch_abi_version;
@@ -2518,6 +2519,18 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
 	return NOTIFY_OK;
 }
 
+static int gpio_device_unregistered_notify(struct notifier_block *nb,
+					   unsigned long action, void *data)
+{
+	struct gpio_chardev_data *cdev = container_of(nb,
+						      struct gpio_chardev_data,
+						      device_unregistered_nb);
+
+	wake_up_poll(&cdev->wait, EPOLLIN | EPOLLERR);
+
+	return NOTIFY_OK;
+}
+
 static __poll_t lineinfo_watch_poll_unlocked(struct file *file,
 					     struct poll_table_struct *pollt)
 {
@@ -2672,17 +2685,27 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	if (ret)
 		goto out_free_bitmap;
 
+	cdev->device_unregistered_nb.notifier_call =
+					gpio_device_unregistered_notify;
+	ret = blocking_notifier_chain_register(&gdev->device_notifier,
+					       &cdev->device_unregistered_nb);
+	if (ret)
+		goto out_unregister_line_notifier;
+
 	file->private_data = cdev;
 
 	ret = nonseekable_open(inode, file);
 	if (ret)
-		goto out_unregister_notifier;
+		goto out_unregister_device_notifier;
 
 	up_read(&gdev->sem);
 
 	return ret;
 
-out_unregister_notifier:
+out_unregister_device_notifier:
+	blocking_notifier_chain_unregister(&gdev->device_notifier,
+					   &cdev->device_unregistered_nb);
+out_unregister_line_notifier:
 	blocking_notifier_chain_unregister(&gdev->line_state_notifier,
 					   &cdev->lineinfo_changed_nb);
 out_free_bitmap:
@@ -2707,6 +2730,8 @@ static int gpio_chrdev_release(struct inode *inode, struct file *file)
 	struct gpio_device *gdev = cdev->gdev;
 
 	bitmap_free(cdev->watched_lines);
+	blocking_notifier_chain_unregister(&gdev->device_notifier,
+					   &cdev->device_unregistered_nb);
 	blocking_notifier_chain_unregister(&gdev->line_state_notifier,
 					   &cdev->lineinfo_changed_nb);
 	gpio_device_put(gdev);
-- 
2.39.2