--- x/fs/btrfs/extent_io.c
+++ y/fs/btrfs/extent_io.c
@@ -1516,7 +1516,8 @@ done:
 					       PAGE_SIZE, !ret);
 		mapping_set_error(page->mapping, ret);
 	}
-	unlock_page(page);
+	if (PageLocked(page))
+		unlock_page(page);
 	ASSERT(ret <= 0);
 	return ret;
 }