AttributeError: ‘DistributedDataParallel‘ object has no attribute ‘XXXX‘

使用多卡并行训练时，调用model里面的某个子模块时，会报如下错误：
AttributeError: ‘DistributedDataParallel’ object has no attribute ‘xxxx’

class train_model(nn.Module):
    def __init__(self, args):
        .
        .
        .
	def forward(self, x): 
	    x = self.backbone(x)
	    x = self.layer1(x)
	    x = self.layer2(x)
	    .
	    .
	    .

在训练代码中：若采用多卡并行训练，model = nn.DataParallel(train_model)
若想调用backbone之后的结果， x=model.backbone(feats)
则会报错：AttributeError: ‘DistributedDataParallel’ object has no attribute ‘backbone’

此时，model下的子网络结构backbone、layer1、layer2的调用方法会发生改变,如下所示
x=model.module.backbone(feats)

直接调用（不加module）适合单卡训练的情况