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Free threading fixes

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This commit is contained in:
Pablo Galindo Salgado 2025-12-06 19:11:21 +00:00
parent 80133a59ff
commit b0adc30759
2 changed files with 30 additions and 19 deletions
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47
Python/import.c
View file

@ -4250,8 +4250,9 @@ register_lazy_on_parent(PyThreadState *tstate, PyObject *name, PyObject *builtin
}
}
// Release the lock - we only needed it for initialization
// The dict operations below are thread-safe on their own
// Release the lock - we only needed it for initialization.
// The dict operations below use PyDict_SetDefaultRef which uses
// critical sections for thread-safety in free-threaded builds.
_PyImport_ReleaseLock(interp);
Py_INCREF(name);
@ -4283,19 +4284,17 @@ register_lazy_on_parent(PyThreadState *tstate, PyObject *name, PyObject *builtin
}
// Record the child to be added when the parent is imported.
PyObject *lazy_submodules;
if (PyDict_GetItemRef(lazy_modules, parent, &lazy_submodules) < 0) {
// Use PyDict_SetDefaultRef to atomically get-or-create the set,
// avoiding TOCTOU races in free-threaded builds.
PyObject *empty_set = PySet_New(NULL);
if (empty_set == NULL) {
goto done;
}
if (lazy_submodules == NULL) {
lazy_submodules = PySet_New(NULL);
if (lazy_submodules == NULL) {
goto done;
}
if (PyDict_SetItem(lazy_modules, parent, lazy_submodules) < 0) {
Py_DECREF(lazy_submodules);
goto done;
}
PyObject *lazy_submodules;
int setdefault_result = PyDict_SetDefaultRef(lazy_modules, parent, empty_set, &lazy_submodules);
Py_DECREF(empty_set);
if (setdefault_result < 0) {
goto done;
}
assert(PyAnySet_CheckExact(lazy_submodules));
if (PySet_Add(lazy_submodules, child) < 0) {
@ -4357,11 +4356,15 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
_PyInterpreterFrame *frame = _PyEval_GetFrame();
assert(frame != NULL && frame->f_globals == frame->f_locals); // should only be called in global scope
// Check if the filter disables the lazy import
// Check if the filter disables the lazy import.
// We must hold a reference to the filter while calling it to prevent
// use-after-free if another thread replaces it via PyImport_SetLazyImportsFilter.
PyObject *filter = FT_ATOMIC_LOAD_PTR_RELAXED(LAZY_IMPORTS_FILTER(interp));
Py_XINCREF(filter);
if (filter != NULL) {
PyObject *modname;
if (PyDict_GetItemRef(globals, &_Py_ID(__name__), &modname) < 0) {
Py_DECREF(filter);
Py_DECREF(abs_name);
return NULL;
} else if (modname == NULL) {
@ -4376,6 +4379,7 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
);
Py_DECREF(modname);
Py_DECREF(filter);
if (res == NULL) {
Py_DECREF(abs_name);
@ -4408,15 +4412,20 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
return NULL;
}
// Add the module name to sys.lazy_modules set (PEP 810)
PyObject *lazy_modules_set = interp->imports.lazy_modules_set;
// Add the module name to sys.lazy_modules set (PEP 810).
// We must hold a reference to the set while using it to prevent
// use-after-free if another thread clears it during interpreter shutdown.
PyObject *lazy_modules_set = FT_ATOMIC_LOAD_PTR_RELAXED(interp->imports.lazy_modules_set);
Py_XINCREF(lazy_modules_set);
if (lazy_modules_set != NULL) {
assert(PyAnySet_CheckExact(lazy_modules_set));
if (PySet_Add(lazy_modules_set, abs_name) < 0) {
Py_DECREF(lazy_modules_set);
Py_DECREF(res);
Py_DECREF(abs_name);
return NULL;
}
Py_DECREF(lazy_modules_set);
}
Py_DECREF(abs_name);
@ -4782,9 +4791,11 @@ PyImport_SetLazyImportsFilter(PyObject *filter)
PyInterpreterState *interp = _PyInterpreterState_GET();
#ifdef Py_GIL_DISABLED
// exchange just in case another thread did same thing at same time
// Exchange the filter atomically. Use deferred DECREF to prevent
// use-after-free: another thread may have loaded the old filter
// and be about to INCREF it.
PyObject *old = _Py_atomic_exchange_ptr(&LAZY_IMPORTS_FILTER(interp), Py_XNewRef(filter));
Py_XDECREF(old);
_PyObject_XDecRefDelayed(old);
#else
Py_XSETREF(LAZY_IMPORTS_FILTER(interp), Py_XNewRef(filter));
#endif

2
Python/sysmodule.c
View file

@ -2908,7 +2908,7 @@ sys_get_lazy_modules_impl(PyObject *module)
/*[clinic end generated code: output=4c641f8881ba87c0 input=511b3a9682c09282]*/
{
PyInterpreterState *interp = _PyInterpreterState_GET();
PyObject *lazy_modules_set = interp->imports.lazy_modules_set;
PyObject *lazy_modules_set = FT_ATOMIC_LOAD_PTR_RELAXED(interp->imports.lazy_modules_set);
if (lazy_modules_set == NULL) {
return PySet_New(NULL);
}