Remove FSDP wrapping from sub-models. (#34452)

* Remove FSDP wrapping from sub-models.

* solve conflict trainer.py

* make fixup

* add unit test for fsdp_auto_wrap_policy when using auto_find_batch_size

* put back extract_model_from_parallel

* use transformers unwrap_model

src/transformers/trainer.py

@@ -66,7 +66,7 @@
 from .integrations.deepspeed import deepspeed_init, deepspeed_load_checkpoint, is_deepspeed_available
 from .integrations.tpu import tpu_spmd_dataloader
 from .modelcard import TrainingSummary
-from .modeling_utils import PreTrainedModel, load_sharded_checkpoint
+from .modeling_utils import PreTrainedModel, load_sharded_checkpoint, unwrap_model
 from .models.auto.modeling_auto import (
     MODEL_FOR_CAUSAL_LM_MAPPING_NAMES,
     MODEL_MAPPING_NAMES,
@@ -2277,8 +2277,11 @@ def _inner_training_loop(
         # FSDP-XLA, SageMaker MP/DP, DataParallel, IPEX
         use_accelerator_prepare = True if model is self.model else False
 
-        # configure fsdp plugin for qlora if any
-        if use_accelerator_prepare:
+        if use_accelerator_prepare and self.is_fsdp_enabled:
+            # In case of auto_find_batch_size=True
+            # Remove FSDP wrapping from sub-models.
+            self.model = unwrap_model(self.model, recursive=True)
+            # configure fsdp plugin for qlora if any
             self._fsdp_qlora_plugin_updates()
 
         if delay_optimizer_creation:

tests/trainer/test_trainer_fsdp.py

@@ -117,6 +117,33 @@ def test_trainer(self):
         execute_subprocess_async(cmd, env=self.get_env())
         # successful return here == success - any errors would have caused an error in the sub-call
 
+    class TestFSDPTrainerWrap(TestCasePlus):
+        @require_accelerate
+        @require_torch_multi_gpu
+        @require_fsdp
+        def test_trainer(self):
+            output_dir = self.get_auto_remove_tmp_dir()
+            cmd = [
+                "accelerate",
+                "launch",
+                "--use_fsdp",
+                "--main_process_port",
+                f"{get_torch_dist_unique_port()}",
+                "--num_processes",
+                f"{torch.cuda.device_count()}",
+                "--fsdp_transformer_layer_cls_to_wrap",
+                "GPT2Block",
+                f"{self.test_file_dir}/test_trainer_fsdp.py",
+                "--output_dir",
+                f"{output_dir}",
+                "--report_to",
+                "none",
+                "--auto_find_batch_size",
+                "True",
+            ]
+            execute_subprocess_async(cmd, env=self.get_env())
+            # successful return here == success - any errors would have caused an error in the sub-call
+
 
 if __name__ == "__main__":
     parser = HfArgumentParser((Seq2SeqTrainingArguments,))