MegaScale discovery is ran twice again

[tengyifei]

One of the PyTorch/XLA operations used by https://github.com/AI-Hypercomputer/torchprime Llama is triggering JAX MegaScale discovery again. This bug tracks identifying that operation and removing the jax_env_context workaround.

[ysiraichi]

Could you either provide more context or label this issue accordingly?

[tengyifei]

Basically PyTorch/XLA uses JAX for pallas kernels etc. It's really easy to accidentally trigger JAX backend initialization. When PyTorch/XLA already initialized its own TPU backend and JAX also tries to initialize its own TPU backend, the second initialization will hang in multi-slice (DCN network) environments. We have seen this bug again and again and this is the latest incarnation.