media: mc: mark the media devnode as registered from the, start

First the media device node was created, and if successful it was
marked as 'registered'. This leaves a small race condition where
an application can open the device node and get an error back
because the 'registered' flag was not yet set.

Change the order: first set the 'registered' flag, then actually
register the media device node. If that fails, then clear the flag.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Fixes: cf4b9211 ("[media] media: Media device node support")
Cc: stable@vger.kernel.org
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

drivers/media/mc/mc-devnode.c

@@ -245,15 +245,14 @@ int __must_check media_devnode_register(struct media_device *mdev,
 	kobject_set_name(&devnode->cdev.kobj, "media%d", devnode->minor);
 
 	/* Part 3: Add the media and char device */
+	set_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
 	ret = cdev_device_add(&devnode->cdev, &devnode->dev);
 	if (ret < 0) {
+		clear_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
 		pr_err("%s: cdev_device_add failed\n", __func__);
 		goto cdev_add_error;
 	}
 
-	/* Part 4: Activate this minor. The char device can now be used. */
-	set_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
-
 	return 0;
 
 cdev_add_error: