Describe the bug

Errror:

raise RuntimeError(f"NCCL error: {error_str}")
RuntimeError: NCCL error: unhandled system error (run with NCCL_DEBUG=INFO for details)

The error goes away with NCCL_SHM_DISABLE=1.

Steps/Code to reproduce bug

uv run pytest tests/unit/models/generation/test_vllm_generation.py::test_vllm_refit_non_collocated_handles_update

Expected behavior

A clear and concise description of what you expected to happen.

Environment overview (please complete the following information)

• Environment location: [Bare-metal, Docker, Cloud(specify cloud provider - AWS, Azure, GCP, Collab)]
• Method of install: [pip install or from source]. Please specify exact commands you used to install.
• If method of install is [Docker], provide docker pull & docker run commands used

Environment details

If NVIDIA docker image is used you don't need to specify these.
Otherwise, please provide:

• OS version
• PyTorch version
• Python version

Additional context

Add any other context about the problem here.
Example: GPU model