mmcv 报错undefined symbol: _ZNK2at6Tensor7is_cudaEv

>>> from mmcv.ops import nms
Traceback (most recent call last):
  File "", line 1, in
  File "/root/.local/lib/python3.7/site-packages/mmcv/ops/__init__.py", line 2, in
    from .assign_score_withk import assign_score_withk
  File "/root/.local/lib/python3.7/site-packages/mmcv/ops/assign_score_withk.py", line 6, in
    '_ext', ['assign_score_withk_forward', 'assign_score_withk_backward'])
  File "/root/.local/lib/python3.7/site-packages/mmcv/utils/ext_loader.py", line 13, in load_ext
    ext = importlib.import_module('mmcv.' + name)
  File "/root/.local/conda/envs/open-mmlab/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
ImportError: /root/.local/lib/python3.7/site-packages/mmcv/_ext.cpython-37m-x86_64-linux-gnu.so: undefined symbol: _ZNK2at6Tensor7is_cudaEv

出现这样的错误主要是由于安装mmcv的时候需要对torch版本和cuda版本同时进行限制，

https://download.openmmlab.com/mmcv/dist/cu101/torch1.5.0/index.html

如上面的链接：

需要设置好cuda版本、torch版本进行下载