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FSDP Extra State Checkpoint Ignored

A regression in PyTorch 2.3's Distributed Checkpoint (DCP) logic stripped the processing of the `_extra_state` dictionary during `set_model_state_dict`.

Quick answer

A regression in PyTorch 2.

Root cause
A regression in PyTorch 2.3's Distributed Checkpoint (DCP) logic stripped the processing of the `_extra_state` dictionary during `set_model_state_dict`.
Recommended fix
Upgrade to PyTorch 2.3.1 where the cherry-pick patch #122946 was applied. - pip install --upgrade torch
How Denpex helps
Denpex matches FSDP Extra State Checkpoint Ignored across every rank in a distributed run and reports which rank failed first, so you act on the initiating node instead of the loudest one.
Model#fsdp#user-report

What this failure is

FSDP Extra State Checkpoint Ignored is a Model failure seen during ML training runs. A regression in PyTorch 2.3's Distributed Checkpoint (DCP) logic stripped the processing of the `_extra_state` dictionary during `set_model_state_dict`. Common tags: Fsdp, User Report.

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Why it happens (the mechanism)

Since the `load_state_dict` call does not throw an exception, engineers assume the checkpoint is loaded correctly and blame the data loader or learning rate scheduler for the divergence.

What you'll observe

  • Model loads successfully without explicit crashing, but training loss diverges immediately.
  • FP8 scaling metadata is lost upon resuming.

Common symptoms and what they mean

SymptomWhy it happens
set_model_state_dict errors on compiled moduleA regression in PyTorch 2.3's Distributed Checkpoint (DCP) logic stripped the processing of the `_extra_state` dictionary during `set_model_state_dict`.
Transformer Engine Checkpointing Broken on Torch 2.3A regression in PyTorch 2.3's Distributed Checkpoint (DCP) logic stripped the processing of the `_extra_state` dictionary during `set_model_state_dict`.

Which systems are affected

  • PyTorch
  • FSDP
  • TransformerEngine

How to confirm this is the problem

Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.

  • Check PyTorch version (`torch.__version__ == '2.3.0'`).
  • Inspect the loaded state dictionary to verify the presence of custom extra state metadata.

The fix and the prevention pattern

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Diagnose this failure in VS Code

Select the traceback or open the failed terminal, then run Denpex locally to see the initiating rank, collateral failures, exact fix, and verification command without uploading the log.

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Root cause

  • A regression in PyTorch 2.3's Distributed Checkpoint (DCP) logic stripped the processing of the `_extra_state` dictionary during `set_model_state_dict`.

The fix and how to prevent it

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