[3.13] gh-117657: Fix race involving immortalizing objects (GH-119927) (#120005)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see gh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.

(cherry picked from commit 47fb4327b5c405da6df066dcaa01b7c1aefab313)

1 files changed, 9 insertions, 15 deletions

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 129c136..8c65b80 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -1965,24 +1965,18 @@ get_py_thread_id(PyObject *self, PyObject *Py_UNUSED(ignored))
 #endif
 
 static PyObject *
-set_immortalize_deferred(PyObject *self, PyObject *value)
+suppress_immortalization(PyObject *self, PyObject *value)
 {
 #ifdef Py_GIL_DISABLED
-    PyInterpreterState *interp = PyInterpreterState_Get();
-    int old_enabled = interp->gc.immortalize.enabled;
-    int old_enabled_on_thread = interp->gc.immortalize.enable_on_thread_created;
-    int enabled_on_thread = 0;
-    if (!PyArg_ParseTuple(value, "i|i",
-                          &interp->gc.immortalize.enabled,
-                          &enabled_on_thread))
-    {
+    int suppress = PyObject_IsTrue(value);
+    if (suppress < 0) {
         return NULL;
     }
-    interp->gc.immortalize.enable_on_thread_created = enabled_on_thread;
-    return Py_BuildValue("ii", old_enabled, old_enabled_on_thread);
-#else
-    return Py_BuildValue("OO", Py_False, Py_False);
+    PyInterpreterState *interp = PyInterpreterState_Get();
+    // Subtract two to suppress immortalization (so that 1 -> -1)
+    _Py_atomic_add_int(&interp->gc.immortalize, suppress ? -2 : 2);
 #endif
+    Py_RETURN_NONE;
 }
 
 static PyObject *
@@ -1990,7 +1984,7 @@ get_immortalize_deferred(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
 #ifdef Py_GIL_DISABLED
     PyInterpreterState *interp = PyInterpreterState_Get();
-    return PyBool_FromLong(interp->gc.immortalize.enable_on_thread_created);
+    return PyBool_FromLong(_Py_atomic_load_int(&interp->gc.immortalize) >= 0);
 #else
     Py_RETURN_FALSE;
 #endif
@@ -2110,7 +2104,7 @@ static PyMethodDef module_functions[] = {
 #ifdef Py_GIL_DISABLED
     {"py_thread_id", get_py_thread_id, METH_NOARGS},
 #endif
-    {"set_immortalize_deferred", set_immortalize_deferred, METH_VARARGS},
+    {"suppress_immortalization", suppress_immortalization, METH_O},
     {"get_immortalize_deferred", get_immortalize_deferred, METH_NOARGS},
 #ifdef _Py_TIER2
     {"uop_symbols_test", _Py_uop_symbols_test, METH_NOARGS},