diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 08d14df..4804872 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -140,14 +140,16 @@
 		spin_unlock(&dev->count_lock);
 	}
 out:
-	mutex_lock(&dev->struct_mutex);
-	if (minor->type == DRM_MINOR_LEGACY) {
-		BUG_ON((dev->dev_mapping != NULL) &&
-			(dev->dev_mapping != inode->i_mapping));
-		if (dev->dev_mapping == NULL)
-			dev->dev_mapping = inode->i_mapping;
+	if (!retcode) {
+		mutex_lock(&dev->struct_mutex);
+		if (minor->type == DRM_MINOR_LEGACY) {
+			if (dev->dev_mapping == NULL)
+				dev->dev_mapping = inode->i_mapping;
+			else if (dev->dev_mapping != inode->i_mapping)
+				retcode = -ENODEV;
+		}
+		mutex_unlock(&dev->struct_mutex);
 	}
-	mutex_unlock(&dev->struct_mutex);
 
 	return retcode;
 }