fix bugs with trainer (#24134)

* fix the deepspeed test failures

* apex fix

* FSDP save ckpt fix

* Update src/transformers/trainer.py

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

---------

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

src/transformers/trainer.py

@@ -1749,7 +1749,16 @@ def _inner_training_loop(
 
         # prepare using `accelerator` prepare
         if use_accelerator_prepare:
-            model, self.optimizer = self.accelerator.prepare(self.model, self.optimizer)
+            if hasattr(self.lr_scheduler, "step"):
+                if self.use_apex:
+                    model = self.accelerator.prepare(self.model)
+                else:
+                    model, self.optimizer = self.accelerator.prepare(self.model, self.optimizer)
+            else:
+                # to handle cases wherein we pass "DummyScheduler" such as when it is specified in DeepSpeed config.
+                model, self.optimizer, self.lr_scheduler = self.accelerator.prepare(
+                    self.model, self.optimizer, self.lr_scheduler
+                )
 
         if self.is_fsdp_enabled:
             self.model = model
@@ -2841,6 +2850,7 @@ def save_model(self, output_dir: Optional[str] = None, _internal_call: bool = Fa
             or self.is_fsdp_enabled
         ):
             if self.is_fsdp_enabled:
+                os.makedirs(output_dir, exist_ok=True)
                 self.accelerator.state.fsdp_plugin.save_model(self.accelerator, self.model, output_dir)
             else:
                 state_dict = self.model.state_dict()