I train a model on two gpus, and then save the model like this:
    net = nn.DataParallel(net)
    .....
    torch.save(net, save_path)

Then I load the model and run inference with single gpu:
   CUDA_VISIBLE_DEIVCES=0 python infer.py

the infer.py is like this:
    im = cv2.imread('./cropped.jpg')
    im = cv2.resize(im, (224, 224)).transpose(2, 0, 1)
    im = torch.tensor([im, im, im], dtype = torch.float32)
    model_path = './res/model.pytorch'
    model = torch.load(model_path)
    model.eval()

    out = model(im).detach().cpu().numpy()

I met the error message like this:
    test()
  File "infer.py", line 25, in test
    out = model(im).detach().cpu().numpy()
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/modules/module.py", line 491, in __call__
    result = self.forward(*input, **kwargs)
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/data_parallel.py", line 110, in forward
    inputs, kwargs = self.scatter(inputs, kwargs, self.device_ids)
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/data_parallel.py", line 121, in scatter
    return scatter_kwargs(inputs, kwargs, device_ids, dim=self.dim)
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/scatter_gather.py", line 36, in scatter_kwargs
    inputs = scatter(inputs, target_gpus, dim) if inputs else []
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/scatter_gather.py", line 29, in scatter
    return scatter_map(inputs)
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/scatter_gather.py", line 16, in scatter_map
    return list(zip(*map(scatter_map, obj)))
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/scatter_gather.py", line 14, in scatter_map
    return Scatter.apply(target_gpus, None, dim, obj)
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/_functions.py", line 73, in forward
    streams = [_get_stream(device) for device in ctx.target_gpus]
  File "/home/zhangzy/.local/lib/python2.7/site-packages/torch/nn/parallel/_functions.py", line 100, in _get_stream
    if _streams[device] is None:
IndexError: list index out of range

What is wrong with this code then?