aio-libs / multidict / 35515167561

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Drop dead retry loop in md_clone_from_ht and fix suspend comments (#1486)

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## What do these changes do?

An automated review of #1484 flagged `md_readonly_find_next()`'s
allocation
as a potential use-after-free, reasoning that a blocking
`PyMem_Malloc()`
call could transiently suspend the held critical section. That mechanism
does not exist: per #1469, `PyMem_Malloc()` never suspends an acquired
critical section on the free-threaded build, so the finding was a false
positive there.

Chasing the same claim through the rest of `hashtable.h` turned up two
real issues. `md_clone_from_ht()` still carried the exact
retry-on-staleness loop #1469 already proved dead in `_md_resize()`,
just
never cleaned up here; this drops it the same way. `_md_del_at()`,
`_md_del_at_for_upd()` and `_md_replace()` have a real suspension risk
(a decref of the old key/value can run a finalizer or weakref callback),
but their comments wrongly attributed it to "the same allocator lock as
`PyMem_Malloc()`", pointing at a comment that no longer exists anywhere
in
the file after #1469; reworded those to name the actual mechanism.

## Are there changes in behavior for the user?

No.

## Is it a substantial burden for the maintainers to support this?

No; this only touches internal comments and removes unreachable code in
one free-threaded-only helper.

## Related issue number

Related to #1484 and #1469, not closing either.

## Checklist

- [x] I think the code is well written
- [ ] Unit tests for the changes exist -- N/A, no behavior change; the
      touched paths are already exercised by the existing suite on both
      backends
- [x] Documentation reflects the changes
- [ ] If you provide code modification, please add yourself to
`CONTRIBUTORS.txt` -- N/A, no such file in this repo
- [x] Add a new news fragment into the `CHANGES/` folder
- [x] `make doc-spelling` passes and any new technical words are added
to `docs/spelling_wordlist.txt... (continued)

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