code: def pre_backward(self, loss: Tensor) -> Tensor:
      return loss
  
file_path: ColossalAI/colossalai/amp/naive_amp/mixed_precision_mixin/bf16.py
imports: import torch
  from torch import Tensor
  from .base import MixedPrecisionMixin
label_desc: Use image node_id 1 for calling the BF16MixedPrecisionMixin obj's underlying member method code with example usage: obj.pre_backward(loss) and returns: loss