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Title: gh-151763: Fix OOM cleanup of initial thread state by zainnadeem786 · Pull Request #152165 · python/cpython · GitHub

Open Graph Title: gh-151763: Fix OOM cleanup of initial thread state by zainnadeem786 · Pull Request #152165 · python/cpython

X Title: gh-151763: Fix OOM cleanup of initial thread state by zainnadeem786 · Pull Request #152165 · python/cpython

Description: Summary This PR addresses OOM-0020 from gh-151763. It fixes a free-threaded crash during interpreter creation when memory allocation fails after the preallocated initial thread state has been selected but before init_threadstate() initializes its interpreter back-pointer. Issue In the free-threaded build, _interpreters.create(reqrefs=True) can fail during early thread-state allocation setup. The affected path is: _interpreters.create(reqrefs=True) -> _interpreters_create_impl() -> _PyXI_NewInterpreter() -> Py_NewInterpreterFromConfig() -> new_interpreter() -> _PyThreadState_New() -> new_threadstate() -> alloc_threadstate() -> _Py_qsbr_reserve() / _Py_ReserveTLBCIndex() -> free_threadstate() For the initial thread state, alloc_threadstate() obtains memory embedded in PyInterpreterState rather than heap-allocated memory. However, if a later free-threaded allocation fails before init_threadstate() runs, cleanup reaches free_threadstate() while tstate->base.interp is still unset. As a result, free_threadstate() fails to recognize the preallocated initial thread state and may incorrectly call PyMem_RawFree() on embedded memory. This can result in: _PyMem_DebugRawFree: bad ID in debug builds access violation in release builds Fix Initialize the interpreter back-pointer earlier in alloc_threadstate(): tstate->base.interp = interp; This ensures that cleanup paths can correctly identify the preallocated initial thread state even if a later allocation fails before init_threadstate() is reached. The successful path remains unchanged because init_threadstate() already sets the same value later. Validation Validated locally on Windows. Builds completed successfully: PCbuild\build.bat -p x64 -c Debug --disable-gil PCbuild\build.bat -p x64 -c Release --disable-gil PCbuild\build.bat -p x64 -c Debug Before the fix, the OOM-0020 reproducer crashed in the free-threaded build with: _PyMem_DebugRawFree: bad ID After the fix, the same allocation-failure path reaches MemoryError instead of crashing. Focused tests passed: PCbuild/amd64t/python_d.exe -m test test__interpreters PCbuild/amd64/python_d.exe -m test test__interpreters git diff --check also passes. Regression Test No regression test is included. The reproducer depends on _testcapi.set_nomemory() in a free-threaded build, and the exact allocation index is build-sensitive. This follows the recent maintainer direction for these OOM-path fixes, where a focused code fix is preferable to fragile allocation-index regression tests. Compatibility This is a localized initialization-order fix for an OOM cleanup path. Normal successful interpreter creation keeps the same final state, because init_threadstate() already assigns the same interpreter pointer later. Addresses OOM-0020 from gh-151763.

Open Graph Description: Summary This PR addresses OOM-0020 from gh-151763. It fixes a free-threaded crash during interpreter creation when memory allocation fails after the preallocated initial thread state has been selec...

X Description: Summary This PR addresses OOM-0020 from gh-151763. It fixes a free-threaded crash during interpreter creation when memory allocation fails after the preallocated initial thread state has been selec...

Opengraph URL: https://github.com/python/cpython/pull/152165

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