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Subject[PATCH 20/23] gpio: sysfs: fix race between gpiod export and unexport
Date
Make sure to deregister the class device (and release the irq) while
holding the sysfs lock in gpio_unexport to prevent racing with
gpio_export.

Note that this requires the recently introduced per-gpio locking to
avoid a deadlock with the kernfs active protection when waiting for the
attribute operations to drain during deregistration.

Signed-off-by: Johan Hovold <johan@kernel.org>
---
drivers/gpio/gpiolib-sysfs.c | 51 ++++++++++++++++++++++----------------------
1 file changed, 26 insertions(+), 25 deletions(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 19c4351021d9..5eee3d0b3a81 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -659,9 +659,8 @@ EXPORT_SYMBOL_GPL(gpiod_export_link);
*/
void gpiod_unexport(struct gpio_desc *desc)
{
- struct gpiod_data *data;
- int status = 0;
- struct device *dev = NULL;
+ struct gpiod_data *data;
+ struct device *dev;

if (!desc) {
pr_warn("%s: invalid GPIO\n", __func__);
@@ -670,33 +669,35 @@ void gpiod_unexport(struct gpio_desc *desc)

mutex_lock(&sysfs_lock);

- if (test_bit(FLAG_EXPORT, &desc->flags)) {
+ if (!test_bit(FLAG_EXPORT, &desc->flags))
+ goto err_unlock;

- dev = class_find_device(&gpio_class, NULL, desc, match_export);
- if (dev) {
- clear_bit(FLAG_SYSFS_DIR, &desc->flags);
- clear_bit(FLAG_EXPORT, &desc->flags);
- } else
- status = -ENODEV;
- }
+ dev = class_find_device(&gpio_class, NULL, desc, match_export);
+ if (!dev)
+ goto err_unlock;
+
+ data = dev_get_drvdata(dev);
+
+ clear_bit(FLAG_SYSFS_DIR, &desc->flags);
+ clear_bit(FLAG_EXPORT, &desc->flags);
+
+ device_unregister(dev);
+
+ /*
+ * Release irq after deregistration to prevent race with edge_store.
+ */
+ if (desc->flags & GPIO_TRIGGER_MASK)
+ gpio_sysfs_free_irq(dev);

mutex_unlock(&sysfs_lock);

- if (dev) {
- data = dev_get_drvdata(dev);
- device_unregister(dev);
- /*
- * Release irq after deregistration to prevent race with
- * edge_store.
- */
- if (desc->flags & GPIO_TRIGGER_MASK)
- gpio_sysfs_free_irq(dev);
- put_device(dev);
- kfree(data);
- }
+ put_device(dev);
+ kfree(data);

- if (status)
- gpiod_dbg(desc, "%s: status %d\n", __func__, status);
+ return;
+
+err_unlock:
+ mutex_unlock(&sysfs_lock);
}
EXPORT_SYMBOL_GPL(gpiod_unexport);

--
2.0.5


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