Quiet TSAN warnings about remaining non-atomic accesses of tstate->state

mpage · mpage · commit c309c6651f9f · 2024-04-22T16:01:20.000-07:00
These should be the last instances of TSAN warning of data races when accessing `tstate->state` non-atomically. TSAN reports a race between accessing `tstate->state` in `_PyThreadState_Suspend()` and the compare/exhange in `park_detached_threads`. This is a false positive due to TSAN modeling failed compare/exchange operations as writes. TSAN reports a race between accessing `tstate->state` in `_PySemaphore_Wait()` and the compare/exchange in `park_detached_threads`. This is the same issue that we saw in pythongh-117830.
diff --git a/Python/parking_lot.c b/Python/parking_lot.c
@@ -194,7 +194,8 @@ _PySemaphore_Wait(_PySemaphore *sema, PyTime_t timeout, int detach)
     PyThreadState *tstate = NULL;
     if (detach) {
         tstate = _PyThreadState_GET();
-        if (tstate && tstate->state == _Py_THREAD_ATTACHED) {
+        if (tstate && _Py_atomic_load_int_relaxed(&tstate->state) ==
+                          _Py_THREAD_ATTACHED) {
             // Only detach if we are attached
             PyEval_ReleaseThread(tstate);
         }
diff --git a/Python/pystate.c b/Python/pystate.c
@@ -2096,7 +2096,7 @@ _PyThreadState_Suspend(PyThreadState *tstate)
 {
     _PyRuntimeState *runtime = &_PyRuntime;
 
-    assert(tstate->state == _Py_THREAD_ATTACHED);
+    assert(_Py_atomic_load_int_relaxed(&tstate->state) == _Py_THREAD_ATTACHED);
 
     struct _stoptheworld_state *stw = NULL;
     HEAD_LOCK(runtime);

Original file line number	Diff line number	Diff line change
`@@ -2096,7 +2096,7 @@ _PyThreadState_Suspend(PyThreadState *tstate)`
`2096`	`2096`	`{`
`2097`	`2097`	`_PyRuntimeState *runtime = &_PyRuntime;`
`2098`	`2098`
`2099`		`- assert(tstate->state == _Py_THREAD_ATTACHED);`
	`2099`	`+ assert(_Py_atomic_load_int_relaxed(&tstate->state) == _Py_THREAD_ATTACHED);`
`2100`	`2100`
`2101`	`2101`	`struct _stoptheworld_state *stw = NULL;`
`2102`	`2102`	`HEAD_LOCK(runtime);`