[BUG] DLPack implementation doesn't handle nullptr for strides

[kkraus14]

According to DLPack spec if the strides attribute is NULL it indicates a dense tensor (https://github.com/dmlc/dlpack/blob/master/include/dlpack/dlpack.h#L142).

The current implementation in cupy will cause a segfault if mem.dlm_tensor.dl_tensor.strides is null as it will try to index into it (https://github.com/cupy/cupy/blob/v6.0.0b3/cupy/core/dlpack.pyx#L236).

[kmaehashi]

Thanks for pointing this out!
Just out of curiosity, do you know any framework that uses strides == NULL?

[kkraus14]

Thanks for pointing this out!
Just out of curiosity, do you know any framework that uses strides == NULL?

We recently added support for DLPack in rapidsai/cudf#1159 and originally used null pointers for dense buffers which is what led to us discovering this issue. We switched it accordingly, but I imagine others implementing DLPack based on the spec could make the same issue.

[crcrpar]

Thank you for your response very much and kudos to

We switched it accordingly