gh-120321: Fix TSan reported race in gen_clear_frame (gh-142995)

colesbury · web-flow · commit 4ea3c1a04747 · 2025-12-19T17:33:49.000-05:00
TSan treats compare-exchanges that fail as if they are writes
so there is a false positive with the read of gi_frame_state in
gen_close.
diff --git a/Objects/genobject.c b/Objects/genobject.c
@@ -153,7 +153,7 @@ _PyGen_Finalize(PyObject *self)
 static void
 gen_clear_frame(PyGenObject *gen)
 {
-    assert(gen->gi_frame_state == FRAME_CLEARED);
+    assert(FT_ATOMIC_LOAD_INT8_RELAXED(gen->gi_frame_state) == FRAME_CLEARED);
     _PyInterpreterFrame *frame = &gen->gi_iframe;
     frame->previous = NULL;
     _PyFrame_ClearExceptCode(frame);

Original file line number	Diff line number	Diff line change
`@@ -153,7 +153,7 @@ _PyGen_Finalize(PyObject *self)`
`153`	`153`	`static void`
`154`	`154`	`gen_clear_frame(PyGenObject *gen)`
`155`	`155`	`{`
`156`		`- assert(gen->gi_frame_state == FRAME_CLEARED);`
	`156`	`+ assert(FT_ATOMIC_LOAD_INT8_RELAXED(gen->gi_frame_state) == FRAME_CLEARED);`
`157`	`157`	`_PyInterpreterFrame *frame = &gen->gi_iframe;`
`158`	`158`	`frame->previous = NULL;`
`159`	`159`	`_PyFrame_ClearExceptCode(frame);`