[TPU Spawn] RuntimeError: Cannot re-initialize CUDA in forked subprocess.

[kaushikb11]

🐛 Bug

  File "/home/kaushikbokka/pytorch-lightning/pytorch_lightning/core/hooks.py", line 685, in transfer_batch_to_device
    return move_data_to_device(batch, device)
  File "/home/kaushikbokka/pytorch-lightning/pytorch_lightning/utilities/apply_func.py", line 161, in move_data_to_device
    return apply_to_collection(batch, dtype=dtype, function=batch_to)
  File "/home/kaushikbokka/pytorch-lightning/pytorch_lightning/utilities/apply_func.py", line 84, in apply_to_collection
    return function(data, *args, **kwargs)
  File "/home/kaushikbokka/pytorch-lightning/pytorch_lightning/utilities/apply_func.py", line 158, in batch_to
    return data.to(device, **kwargs)
RuntimeError: Cannot re-initialize CUDA in forked subprocess. To use CUDA with multiprocessing, you must use the 'spawn' start method

Environment

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• IDE: Please, use our python bug_report_model.py template.

• Colab Notebook: Please copy and paste the output from our environment collection script (or fill out the checklist below manually).

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wget https://raw.githubusercontent.com/PyTorchLightning/pytorch-lightning/master/tests/collect_env_details.py
# For security purposes, please check the contents of collect_env_details.py before running it.
python collect_env_details.py

• PyTorch Version (e.g., 1.0):
• OS (e.g., Linux):
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• Build command you used (if compiling from source):
• Python version:
• CUDA/cuDNN version:
• GPU models and configuration:
• Any other relevant information:

Additional context