pythongh-117657: Fix TSAN race in QSBR assertion (python#119887)

colesbury · web-flow · commit 90ec19fd33e2 · 2024-06-01T10:04:38.000-04:00
Due to a limitation in TSAN, all reads from `PyThreadState.state` must be
atomic to avoid reported races.
diff --git a/Python/qsbr.c b/Python/qsbr.c
@@ -160,7 +160,8 @@ qsbr_poll_scan(struct _qsbr_shared *shared)
 bool
 _Py_qsbr_poll(struct _qsbr_thread_state *qsbr, uint64_t goal)
 {
-    assert(_PyThreadState_GET()->state == _Py_THREAD_ATTACHED);
+    assert(_Py_atomic_load_int_relaxed(&_PyThreadState_GET()->state) == _Py_THREAD_ATTACHED);
+
     if (_Py_qbsr_goal_reached(qsbr, goal)) {
         return true;
     }
diff --git a/Tools/tsan/suppressions_free_threading.txt b/Tools/tsan/suppressions_free_threading.txt
@@ -75,8 +75,6 @@ race_top:_PyFrame_GetCode
 race_top:_PyFrame_Initialize
 race_top:PyInterpreterState_ThreadHead
 race_top:_PyObject_TryGetInstanceAttribute
-race_top:_Py_qsbr_unregister
-race_top:_Py_qsbr_poll
 race_top:PyThreadState_Next
 race_top:Py_TYPE
 race_top:PyUnstable_InterpreterFrame_GetLine

Original file line number	Diff line number	Diff line change
`@@ -160,7 +160,8 @@ qsbr_poll_scan(struct _qsbr_shared *shared)`
`160`	`160`	`bool`
`161`	`161`	`_Py_qsbr_poll(struct _qsbr_thread_state *qsbr, uint64_t goal)`
`162`	`162`	`{`
`163`		`- assert(_PyThreadState_GET()->state == _Py_THREAD_ATTACHED);`
	`163`	`+ assert(_Py_atomic_load_int_relaxed(&_PyThreadState_GET()->state) == _Py_THREAD_ATTACHED);`
	`164`	`+`
`164`	`165`	`if (_Py_qbsr_goal_reached(qsbr, goal)) {`
`165`	`166`	`return true;`
`166`	`167`	`}`