Crash with PyGILState_Ensure called from background thread during finalization on Python 3.14.0a7 #132948
Description
Crash report
What happened?
Coming over from work on PyO3's branch to support Python 3.14.
We have a crash which can be narrowed down to calling PyGilState_Ensure in a background thread while finalization is underway. This seems to be new in 3.14.
// src/lib.rs
use pyo3_ffi::*;
static mut MODULE_DEF: PyModuleDef = PyModuleDef {
m_base: PyModuleDef_HEAD_INIT,
m_name: c"pyo3_scratch".as_ptr(),
m_doc: c"Demonstration of PyGILState_Ensure crash.".as_ptr(),
m_size: 0,
m_methods: unsafe { METHODS as *const [PyMethodDef] as *mut PyMethodDef },
m_slots: unsafe { SLOTS as *const [PyModuleDef_Slot] as *mut PyModuleDef_Slot },
m_traverse: None,
m_clear: None,
m_free: None,
};
static mut SLOTS: &[PyModuleDef_Slot] = &[
PyModuleDef_Slot {
slot: Py_mod_gil,
value: Py_MOD_GIL_NOT_USED,
},
unsafe { std::mem::zeroed() },
];
static mut METHODS: &[PyMethodDef] = &[
// A zeroed PyMethodDef to mark the end of the array.
PyMethodDef::zeroed(),
];
// The module initialization function, which must be named `PyInit_<your_module>`.
#[allow(non_snake_case)]
#[no_mangle]
pub unsafe extern "C" fn PyInit_pyo3_scratch() -> *mut PyObject {
std::thread::spawn(|| {
loop {
// Repeatedly acquire and release the GIL;
unsafe {
PyGILState_Release(PyGILState_Ensure());
}
}
});
PyModuleDef_Init(std::ptr::addr_of_mut!(MODULE_DEF))
}# Cargo.toml
[package]
name = "pyo3-scratch"
version = "0.1.0"
edition = "2021"
[lib]
name = "pyo3_scratch"
crate-type = ["cdylib"]
[dependencies]
pyo3-ffi = { version = "0.24" }# pyproject.toml
[build-system]
requires = ["maturin>=1,<2"]
build-backend = "maturin"
[project]
dynamic = ["version"]
name = "pyo3-scratch"
requires-python = ">=3.6"
[tool.maturin]
features = ["pyo3-ffi/extension-module"]Reproduce by
- install the module
python -c "import pyo3_scratch"- observe segfault (not every time)
lldb backtrace:
(lldb) t 2
* thread #2, stop reason = EXC_BAD_ACCESS (code=1, address=0x1d09)
frame #0: 0x0000000100898664 libpython3.14.dylib`_PyThreadState_Attach [inlined] bind_gilstate_tstate(tstate=0x00000001600041c0) at pystate.c:331:48 [opt]
328 // XXX assert(!tstate->_status.active);
329 assert(!tstate->_status.bound_gilstate);
330
-> 331 _PyRuntimeState *runtime = tstate->interp->runtime;
332 PyThreadState *tcur = gilstate_tss_get(runtime);
333 assert(tstate != tcur);
334
(lldb) bt
* thread #2, stop reason = EXC_BAD_ACCESS (code=1, address=0x1d09)
* frame #0: 0x0000000100898664 libpython3.14.dylib`_PyThreadState_Attach [inlined] bind_gilstate_tstate(tstate=0x00000001600041c0) at pystate.c:331:48 [opt]
frame #1: 0x0000000100898660 libpython3.14.dylib`_PyThreadState_Attach [inlined] tstate_activate(tstate=0x00000001600041c0) at pystate.c:2055:9 [opt]
frame #2: 0x0000000100898658 libpython3.14.dylib`_PyThreadState_Attach(tstate=0x00000001600041c0) at pystate.c:2145:9 [opt]
frame #3: 0x00000001008699ec libpython3.14.dylib`PyEval_RestoreThread(tstate=<unavailable>) at ceval_gil.c:654:5 [opt] [artificial]
frame #4: 0x000000010089912c libpython3.14.dylib`PyGILState_Ensure at pystate.c:2840:9 [opt]
frame #5: 0x00000001003a15d4 pyo3_scratch.cpython-314-darwin.so`std::sys::backtrace::__rust_begin_short_backtrace::h0e87d186cf26a828 + 12
frame #6: 0x00000001003a0d44 pyo3_scratch.cpython-314-darwin.so`core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::h10c677eeb05c5f18 + 108
frame #7: 0x00000001003c1710 pyo3_scratch.cpython-314-darwin.so`std::sys::pal::unix::thread::Thread::new::thread_start::h6d53b1b0c047a3b9 + 52
frame #8: 0x000000018d9c9c0c libsystem_pthread.dylib`_pthread_start + 136
CPython versions tested on:
3.14
Operating systems tested on:
macOS
Output from running 'python -VV' on the command line:
Python 3.14.0a7 (main, Apr 25 2025, 15:33:43) [Clang 17.0.0 (clang-1700.0.13.3)]