fix_stage3_fp16 (#39171)

python/paddle/distributed/fleet/meta_parallel/sharding/sharding_stage3.py

@@ -393,6 +393,7 @@ class ShardingStage3(nn.Layer):
                 else:
                     param.bw_storage.scale_(scale=self._world_size_scaling)
             param.fw_storage = _VarBaseWrapper(param)
+            assert param.fw_storage.grad is None
             param.fw_storage._copy_gradient_from(param.bw_storage)
             update_list.append(param)
         return update_list
@@ -495,10 +496,9 @@ class ShardingStage3(nn.Layer):
     def _redefine_opt_step(self):
         params_slice_func = self._update_params_slice
         opt_step = self._optim.step
-        update_scaler = self._optim.update_scaler
 
         def _opt_step(self):
-            if not update_scaler:
+            if not self.update_scaler:
                 params_slice_func()
             if self.offload:
                 with device_guard(device="cpu"):