adding a barrier so that tmp dir stays alive

[uralik]

What does this PR do? Please describe:

ckpt saving was crashing since some ranks attempted to access model tmp dir when it was removed already

Fixes #{issue number}

Does your PR introduce any breaking changes? If yes, please list them: List of all backwards-incompatible changes.

Check list:

• [ ] Was the content of this PR discussed and approved via a GitHub issue? (no need for typos or documentation improvements)
• [ ] Did you read the contributor guideline?
• [ ] Did you make sure that your PR does only one thing instead of bundling different changes together?
• [ ] Did you make sure to update the documentation with your changes? (if necessary)
• [ ] Did you write any new necessary tests?
• [ ] Did you verify new and existing tests pass locally with your changes?
• [ ] Did you update the CHANGELOG? (no need for typos, documentation, or minor internal changes)