gh-151593: Fix dead lock in PyDict insert_split_key()#152200
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Do not hold LOCK_KEYS() lock when calling PyType_Modified() to avoid a deadlock. Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>
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On Python built with
It only takes 1 or 2 iterations to trigger the deadlock. With this change, I can no longer reproduce the deadlock: the test is running for 5 minutes (test_abc passed 35 times in a row). |
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@dpdani @colesbury @nascheme: Would you mind to review this fix? |
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I'd add a comment, but otherwise LGTM 👍
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@dpdani: I added a comment on LOCK_KEYS() based on previous comments on pull requests and issues. Does it look good to you? |
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Thanks for fixing this
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Merged. Thanks for reviews! |
This was referenced Jun 25, 2026
nascheme
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Revert commits:
gh-151593: Fix dead lock in PyDict insert_split_key() (#152200)
gh-150490: Raise PyType_Modified for insertion into split dictionary (#150489)
For gh-150489, it violates locking discipline and results in deadlocks,
gh-151593 is an example of it being hit in CI. The attempted fix
gh-152200 avoids the deadlock but introduces a data-race. The race
window is small but can be triggered with pure Python code.
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Do not hold LOCK_KEYS() lock when calling PyType_Modified() to avoid a deadlock.