gpio: sysfs: fix race between gpiod export and unexport

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>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 1bb05aa..1540f7d 100644 (file)
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -674,9 +674,8 @@ 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__);
@@ -685,33 +684,35 @@ 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);