[PATCH] gpio: sysfs: fix chip removal with GPIOs exported over sysfs

[Bartosz Golaszewski]

Currently if we export a GPIO over sysfs and unbind the parent GPIO
controller, the exported attribute will remain under /sys/class/gpio
because once we remove the parent device, we can no longer associate the
descriptor with it in gpiod_unexport() and never drop the final
reference.

Rework the teardown code: provide an unlocked variant of
gpiod_unexport() and remove all exported GPIOs with the sysfs_lock taken
before unregistering the parent device itself. This is done to prevent
any new exports happening before we unregister the device completely.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>
---
 drivers/gpio/gpiolib-sysfs.c | 106 ++++++++++++++++++-----------------
 1 file changed, 55 insertions(+), 51 deletions(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index cd553acf3055e..d4a46a0a37d8f 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -919,63 +919,68 @@ int gpiod_export_link(struct device *dev, const char *name,
 }
 EXPORT_SYMBOL_GPL(gpiod_export_link);
 
-/**
- * gpiod_unexport - reverse effect of gpiod_export()
- * @desc: GPIO to make unavailable
- *
- * This is implicit on gpiod_free().
- */
-void gpiod_unexport(struct gpio_desc *desc)
+static void gpiod_unexport_unlocked(struct gpio_desc *desc)
 {
 	struct gpiod_data *tmp, *desc_data = NULL;
 	struct gpiodev_data *gdev_data;
 	struct gpio_device *gdev;
 
-	if (!desc) {
-		pr_warn("%s: invalid GPIO\n", __func__);
+	if (!test_bit(GPIOD_FLAG_EXPORT, &desc->flags))
 		return;
-	}
 
-	scoped_guard(mutex, &sysfs_lock) {
-		if (!test_bit(GPIOD_FLAG_EXPORT, &desc->flags))
-			return;
-
-		gdev = gpiod_to_gpio_device(desc);
-		gdev_data = gdev_get_data(gdev);
-		if (!gdev_data)
-			return;
+	gdev = gpiod_to_gpio_device(desc);
+	gdev_data = gdev_get_data(gdev);
+	if (!gdev_data)
+		return;
 
-		list_for_each_entry(tmp, &gdev_data->exported_lines, list) {
-			if (gpiod_is_equal(desc, tmp->desc)) {
-				desc_data = tmp;
-				break;
-			}
+	list_for_each_entry(tmp, &gdev_data->exported_lines, list) {
+		if (gpiod_is_equal(desc, tmp->desc)) {
+			desc_data = tmp;
+			break;
 		}
+	}
 
-		if (!desc_data)
-			return;
+	if (!desc_data)
+		return;
 
-		list_del(&desc_data->list);
-		clear_bit(GPIOD_FLAG_EXPORT, &desc->flags);
+	list_del(&desc_data->list);
+	clear_bit(GPIOD_FLAG_EXPORT, &desc->flags);
 #if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
-		sysfs_put(desc_data->value_kn);
-		device_unregister(desc_data->dev);
-
-		/*
-		 * Release irq after deregistration to prevent race with
-		 * edge_store.
-		 */
-		if (desc_data->irq_flags)
-			gpio_sysfs_free_irq(desc_data);
+	sysfs_put(desc_data->value_kn);
+	device_unregister(desc_data->dev);
+
+	/*
+	 * Release irq after deregistration to prevent race with
+	 * edge_store.
+	 */
+	if (desc_data->irq_flags)
+		gpio_sysfs_free_irq(desc_data);
 #endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
-		sysfs_remove_groups(desc_data->parent,
-				    desc_data->chip_attr_groups);
-	}
+	sysfs_remove_groups(desc_data->parent,
+			    desc_data->chip_attr_groups);
 
 	mutex_destroy(&desc_data->mutex);
 	kfree(desc_data);
 }
+
+/**
+ * gpiod_unexport - reverse effect of gpiod_export()
+ * @desc: GPIO to make unavailable
+ *
+ * This is implicit on gpiod_free().
+ */
+void gpiod_unexport(struct gpio_desc *desc)
+{
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return;
+	}
+
+	guard(mutex)(&sysfs_lock);
+
+	gpiod_unexport_unlocked(desc);
+}
 EXPORT_SYMBOL_GPL(gpiod_unexport);
 
 int gpiochip_sysfs_register(struct gpio_device *gdev)
@@ -1054,29 +1059,28 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 	struct gpio_desc *desc;
 	struct gpio_chip *chip;
 
-	scoped_guard(mutex, &sysfs_lock) {
-		data = gdev_get_data(gdev);
-		if (!data)
-			return;
+	guard(mutex)(&sysfs_lock);
 
-#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
-		device_unregister(data->cdev_base);
-#endif /* CONFIG_GPIO_SYSFS_LEGACY */
-		device_unregister(data->cdev_id);
-		kfree(data);
-	}
+	data = gdev_get_data(gdev);
+	if (!data)
+		return;
 
 	guard(srcu)(&gdev->srcu);
-
 	chip = srcu_dereference(gdev->chip, &gdev->srcu);
 	if (!chip)
 		return;
 
 	/* unregister gpiod class devices owned by sysfs */
 	for_each_gpio_desc_with_flag(chip, desc, GPIOD_FLAG_SYSFS) {
-		gpiod_unexport(desc);
+		gpiod_unexport_unlocked(desc);
 		gpiod_free(desc);
 	}
+
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
+	device_unregister(data->cdev_base);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
+	device_unregister(data->cdev_id);
+	kfree(data);
 }
 
 /*
-- 
2.47.3