Fixing KTO+QLoRA+multi-GPU (#2420)

* WIP

* removing artifacts

* adding error

* adding adapter check

* linting

* simplifying check

* linting v2

* config fix -___-

examples/llama-3/qlora-1b-kto.yaml

@@ -55,7 +55,7 @@ tf32: true
 
 gradient_checkpointing: true
 gradient_checkpointing_kwargs:
-  use_reentrant: true
+  use_reentrant: false
 early_stopping_patience:
 resume_from_checkpoint:
 local_rank:

src/axolotl/utils/config/models/input/v0_4_1/__init__.py

@@ -1679,6 +1679,30 @@ class AxolotlInputConfig(
 
         return data
 
+    @model_validator(mode="before")
+    @classmethod
+    def check_rl_config_gradient_checkpointing(cls, data):
+        # TODO: SalmanMohammadi
+        # Distributed RL with QLoRA + gradient checkpointing
+        # and use_reentrant = True is broken upstream in TRL
+        # pylint: disable=too-many-boolean-expressions
+        if (
+            data.get("rl")
+            and data.get("gradient_checkpointing")
+            and data.get("gradient_checkpointing_kwargs")
+            and data.get("gradient_checkpointing_kwargs").get("use_reentrant")
+            and data.get("load_in_4bit")
+            and data.get("adapter") == "qlora"
+            and data.get("capabilities")
+            and data.get("capabilities").get("n_gpu", 1) > 1
+        ):
+            raise ValueError(
+                "The `use_reentrant: True` implementation of gradient checkpointing "
+                "is not supported for distributed RL training with QLoRA. Please set "
+                "`use_reentrant: False` in `gradient_checkpointing_kwargs`."
+            )
+        return data
+
     @model_validator(mode="before")
     @classmethod
     def check_kto_config(cls, data):
@@ -1689,15 +1713,6 @@ class AxolotlInputConfig(
             if data.get("remove_unused_columns") is not False:
                 raise ValueError("Set `remove_unused_columns: False` when using kto")
 
-            if data.get("gradient_checkpointing") and not (
-                data.get("gradient_checkpointing_kwargs")
-                and isinstance(data.get("gradient_checkpointing_kwargs"), dict)
-                and data["gradient_checkpointing_kwargs"].get("use_reentrant")
-            ):
-                raise ValueError(
-                    "Set `gradient_checkpointing_kwargs: {use_reentrant: true}` for when kto is enabled"
-                )
-
         return data