Compilation is fine. However, there is still an error trying to import the module.
>>> import torch
>>> import cudnn_extension
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: /usr/local/lib/python3.7/dist-packages/cudnn_extension-0.0.0-py3.7-linux-x86_64.egg/cudnn_extension.cpython-37m-x86_64-linux-gnu.so: undefined symbol: cudnnGetErrorString
>>>