Crash in _PyXI_ApplyErrorCode()

[ericsnowcurrently]

Crash report

Bug description:

This is a problem in Python/crossinterp.c, as exposed by the _interpreters module.

reproducer:

1. interp is running as "main" in thread 1
2. thread 2 calls _PyXI_Enter(), which emits the _PyXI_ERR_ALREADY_RUNNING error code
3. thread 1 finishes
4. thread 2 calls _PyXI_ApplyError()
5. _PyXI_ApplyError() calls _PyInterpreterState_FailIfNotRunning() to raise the exception, but it doesn't raise anything

I noticed this while working on gh-126914.

CPython versions tested on:

3.14

Operating systems tested on:

No response

Linked PRs

• gh-126986: Drop _PyInterpreterState_FailIfNotRunning() #126988
• [3.13] gh-126986: Drop _PyInterpreterState_FailIfNotRunning() (gh-126988) #126995
• [3.13] gh-126986: Stop Using _PyInterpreterState_FailIfNotRunning() #127112

[ZeroIntensity]

Affecting 3.13(t) as well:

$ ./python x.py
python: Python/crossinterp.c:988: _PyXI_ApplyErrorCode: Assertion `_PyInterpreterState_IsRunningMain(interp)' failed.