Prevent recursive symlink creation iwhen save_last='link' and save_top_k=-1
#21186
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…in ModelCheckpoint - Added a check in _link_checkpoint to compare absolute paths of filepath and linkpath - Only create symlink if paths differ, avoiding self-linking when save_last='link' and save_top_k=-1 - Updated test to assert the fix prevents the recursive symlink bug
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Pull Request Overview
This PR fixes a bug in PyTorch Lightning's ModelCheckpoint callback where using save_last='link' with save_top_k=-1 creates a recursive symlink that points to itself.
- Adds path comparison logic to prevent self-referencing symlinks in
_link_checkpointmethod - Updates test coverage to verify the fix works correctly
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/lightning/pytorch/callbacks/model_checkpoint.py | Adds absolute path comparison to prevent recursive symlink creation |
| tests/tests_pytorch/callbacks/test_model_checkpoint_additional_cases.py | Adds comprehensive regression test for the symlink bug scenario |
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SkafteNicki
reviewed
Sep 9, 2025
tests/tests_pytorch/callbacks/test_model_checkpoint_additional_cases.py
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Borda
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save_last='link' and save_top_k=-1
SkafteNicki
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Sep 10, 2025
Borda
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Sep 10, 2025
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Fix ModelCheckpoint recursive symlink creation when save_last='link' and save_top_k=-1
What does this PR do?
This PR fixes a bug in PyTorch Lightning's ModelCheckpoint callback where using
save_last='link'withsave_top_k=-1creates a recursive symlink (last.ckpt -> last.ckpt). This occurs when the last checkpoint saved is thelast.ckptfile itself, leading to a self-referencing symlink.Changes Made:
filepathandlinkpathsave_last='link'andsave_top_k=-1This ensures the checkpoint functionality works correctly without creating invalid symlinks, maintaining backward compatibility.
Fixes #21110
No breaking changes introduced.
📚 Documentation preview 📚: https://pytorch-lightning--21186.org.readthedocs.build/en/21186/