old_contents: import torch.nn as nn
  import torch.nn.functional as F
  
  from ..registry import LOSSES
  from .utils import weighted_loss
  
  mse_loss = weighted_loss(F.mse_loss)
  
  
  @LOSSES.register_module
  class MSELoss(nn.Module):
  
      def __init__(self, reduction='mean', loss_weight=1.0):
          super().__init__()
          self.reduction = reduction
          self.loss_weight = loss_weight
  
      def forward(self, pred, target, weight=None, avg_factor=None):
          loss = self.loss_weight * mse_loss(
              pred,
              target,
              weight,
              reduction=self.reduction,
              avg_factor=avg_factor)
          return loss
  
new_contents: import torch.nn as nn
  import torch.nn.functional as F
  
  from ..registry import LOSSES
  from .utils import weighted_loss
  
  
  @weighted_loss
  def mse_loss(pred, target):
      return F.mse_loss(pred, target, reduction='none')
  
  
  @LOSSES.register_module
  class MSELoss(nn.Module):
  
      def __init__(self, reduction='mean', loss_weight=1.0):
          super().__init__()
          self.reduction = reduction
          self.loss_weight = loss_weight
  
      def forward(self, pred, target, weight=None, avg_factor=None):
          loss = self.loss_weight * mse_loss(
              pred,
              target,
              weight,
              reduction=self.reduction,
              avg_factor=avg_factor)
          return loss
  
subject: fix bug of mse_loss (#2301)