[3.13] gh-126312: Don't traverse frozen objects on the free-threaded build (GH-126338) (#126866)

* Fix merge conflicts.

* [3.13] gh-126312: Don't traverse frozen objects on the free-threaded build (GH-126338)

Also, _PyGC_Freeze() no longer freezes unreachable objects.

(cherry picked from commit d4c72fed8cba8e15ab7bb6c30a92bc9f2c8f0a2c)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>

---------

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index bf3cd01..ff86c75 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -111,6 +111,12 @@ worklist_remove(struct worklist_iter *iter)
 }
 
 static inline int
+gc_is_frozen(PyObject *op)
+{
+    return (op->ob_gc_bits & _PyGC_BITS_FROZEN) != 0;
+}
+
+static inline int
 gc_is_unreachable(PyObject *op)
 {
     return (op->ob_gc_bits & _PyGC_BITS_UNREACHABLE) != 0;
@@ -229,7 +235,7 @@ op_from_block(void *block, void *arg, bool include_frozen)
     if (!_PyObject_GC_IS_TRACKED(op)) {
         return NULL;
     }
-    if (!include_frozen && (op->ob_gc_bits & _PyGC_BITS_FROZEN) != 0) {
+    if (!include_frozen && gc_is_frozen(op)) {
         return NULL;
     }
     return op;
@@ -364,7 +370,10 @@ process_delayed_frees(PyInterpreterState *interp)
 static int
 visit_decref(PyObject *op, void *arg)
 {
-    if (_PyObject_GC_IS_TRACKED(op) && !_Py_IsImmortal(op)) {
+    if (_PyObject_GC_IS_TRACKED(op)
+        && !_Py_IsImmortal(op)
+        && !gc_is_frozen(op))
+    {
         // If update_refs hasn't reached this object yet, mark it
         // as (tentatively) unreachable and initialize ob_tid to zero.
         gc_maybe_init_refs(op);
@@ -1419,7 +1428,7 @@ visit_freeze(const mi_heap_t *heap, const mi_heap_area_t *area,
              void *block, size_t block_size, void *args)
 {
     PyObject *op = op_from_block(block, args, true);
-    if (op != NULL) {
+    if (op != NULL && !gc_is_unreachable(op)) {
         op->ob_gc_bits |= _PyGC_BITS_FROZEN;
     }
     return true;
@@ -1464,7 +1473,7 @@ visit_count_frozen(const mi_heap_t *heap, const mi_heap_area_t *area,
                    void *block, size_t block_size, void *args)
 {
     PyObject *op = op_from_block(block, args, true);
-    if (op != NULL && (op->ob_gc_bits & _PyGC_BITS_FROZEN) != 0) {
+    if (op != NULL && gc_is_frozen(op)) {
         struct count_frozen_args *arg = (struct count_frozen_args *)args;
         arg->count++;
     }