fix #3324

Former-commit-id: 5e710c4ac331f3400534d33b2646c4108c898d98

src/llmtuner/model/utils.py

@@ -132,8 +132,9 @@ def gradient_checkpointing_enable(
 
     if "value" in inspect.signature(self._set_gradient_checkpointing).parameters:  # old GC format
         self.apply(partial(self._set_gradient_checkpointing, value=True))
+        self.enable_input_require_grads()
         logger.warning("You are using the old GC format, some features (e.g. BAdam) will be invalid.")
-    else:
+    else:  # have already enabled input require gradients
         self._set_gradient_checkpointing(enable=True, gradient_checkpointing_func=custom_gradient_checkpointing_func)