devdanzin/import_wrong_interpreter.md

Created March 18, 2026 10:06

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import.c: Wrong interpreter on return + double lock release

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import_wrong_interpreter.md

import.c: Wrong interpreter on return + double lock release

Summary

Two critical bugs in the import system:

import_run_extension (line 2189): After switching to main interpreter, _PyUnicode_Copy failure does return NULL instead of goto main_finally. Code resumes on wrong interpreter → crashes/corruption.
_PyImport_LoadLazyImportTstate (line 3931): _PyImport_ReleaseLock called before goto error, then error path releases again → Py_FatalError("unlocking a recursive mutex not owned by current thread").

Fix

Change return NULL at line 2189 to rc = -1; goto main_finally;.
Remove _PyImport_ReleaseLock(interp) at line 3931.

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