pythongh-117657: Fix data races reported by TSAN on interp->threads.main (pythonGH-118865)

mpage · miss-islington · commit 6d5e97f477dd · 2024-05-10T13:59:20.000Z
Use relaxed loads/stores when reading/writing to this field. (cherry picked from commit 22d5185) Co-authored-by: mpage <mpage@meta.com>
diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-05-09-19-47-12.gh-issue-117657.Vn0Yey.rst b/Misc/NEWS.d/next/Core and Builtins/2024-05-09-19-47-12.gh-issue-117657.Vn0Yey.rst
@@ -0,0 +1 @@
+Fix data races on the field that stores a pointer to the interpreter's main thread that occur in free-threaded builds.
diff --git a/Python/pystate.c b/Python/pystate.c
@@ -1038,6 +1038,17 @@ _PyInterpreterState_DeleteExceptMain(_PyRuntimeState *runtime)
 }
 #endif
 
+static inline void
+set_main_thread(PyInterpreterState *interp, PyThreadState *tstate)
+{
+    _Py_atomic_store_ptr_relaxed(&interp->threads.main, tstate);
+}
+
+static inline PyThreadState *
+get_main_thread(PyInterpreterState *interp)
+{
+    return _Py_atomic_load_ptr_relaxed(&interp->threads.main);
+}
 
 int
 _PyInterpreterState_SetRunningMain(PyInterpreterState *interp)
@@ -1052,21 +1063,22 @@ _PyInterpreterState_SetRunningMain(PyInterpreterState *interp)
                         "current tstate has wrong interpreter");
         return -1;
     }
-    interp->threads.main = tstate;
+    set_main_thread(interp, tstate);
+
     return 0;
 }
 
 void
 _PyInterpreterState_SetNotRunningMain(PyInterpreterState *interp)
 {
-    assert(interp->threads.main == current_fast_get());
-    interp->threads.main = NULL;
+    assert(get_main_thread(interp) == current_fast_get());
+    set_main_thread(interp, NULL);
 }
 
 int
 _PyInterpreterState_IsRunningMain(PyInterpreterState *interp)
 {
-    if (interp->threads.main != NULL) {
+    if (get_main_thread(interp) != NULL) {
         return 1;
     }
     // Embedders might not know to call _PyInterpreterState_SetRunningMain(),
@@ -1082,18 +1094,15 @@ int
 _PyThreadState_IsRunningMain(PyThreadState *tstate)
 {
     PyInterpreterState *interp = tstate->interp;
-    if (interp->threads.main != NULL) {
-        return tstate == interp->threads.main;
-    }
     // See the note in _PyInterpreterState_IsRunningMain() about
     // possible false negatives here for embedders.
-    return 0;
+    return get_main_thread(interp) == tstate;
 }
 
 int
 _PyInterpreterState_FailIfRunningMain(PyInterpreterState *interp)
 {
-    if (interp->threads.main != NULL) {
+    if (get_main_thread(interp) != NULL) {
         PyErr_SetString(PyExc_InterpreterError,
                         "interpreter already running");
         return -1;
@@ -1105,8 +1114,8 @@ void
 _PyInterpreterState_ReinitRunningMain(PyThreadState *tstate)
 {
     PyInterpreterState *interp = tstate->interp;
-    if (interp->threads.main != tstate) {
-        interp->threads.main = NULL;
+    if (get_main_thread(interp) != tstate) {
+        set_main_thread(interp, NULL);
     }
 }
 
diff --git a/Tools/tsan/suppressions_free_threading.txt b/Tools/tsan/suppressions_free_threading.txt
@@ -33,8 +33,6 @@ race_top:_mi_heap_delayed_free_partial
 race_top:_PyEval_EvalFrameDefault
 race_top:_PyImport_AcquireLock
 race_top:_PyImport_ReleaseLock
-race_top:_PyInterpreterState_SetNotRunningMain
-race_top:_PyInterpreterState_IsRunningMain
 # https://gist.github.com/mpage/0a24eb2dd458441ededb498e9b0e5de8
 race_top:_PyParkingLot_Park
 race_top:_PyType_HasFeature

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix data races on the field that stores a pointer to the interpreter's main thread that occur in free-threaded builds.`
Original file line number	Diff line number	Diff line change
`@@ -1038,6 +1038,17 @@ _PyInterpreterState_DeleteExceptMain(_PyRuntimeState *runtime)`
`1038`	`1038`	`}`
`1039`	`1039`	`#endif`
`1040`	`1040`
	`1041`	`+static inline void`
	`1042`	`+set_main_thread(PyInterpreterState interp, PyThreadState tstate)`
	`1043`	`+{`
	`1044`	`+ _Py_atomic_store_ptr_relaxed(&interp->threads.main, tstate);`
	`1045`	`+}`
	`1046`	`+`
	`1047`	`+static inline PyThreadState *`
	`1048`	`+get_main_thread(PyInterpreterState *interp)`
	`1049`	`+{`
	`1050`	`+ return _Py_atomic_load_ptr_relaxed(&interp->threads.main);`
	`1051`	`+}`
`1041`	`1052`
`1042`	`1053`	`int`
`1043`	`1054`	`_PyInterpreterState_SetRunningMain(PyInterpreterState *interp)`
`@@ -1052,21 +1063,22 @@ _PyInterpreterState_SetRunningMain(PyInterpreterState *interp)`
`1052`	`1063`	`"current tstate has wrong interpreter");`
`1053`	`1064`	`return -1;`
`1054`	`1065`	`}`
`1055`		`- interp->threads.main = tstate;`
	`1066`	`+ set_main_thread(interp, tstate);`
	`1067`	`+`
`1056`	`1068`	`return 0;`
`1057`	`1069`	`}`
`1058`	`1070`
`1059`	`1071`	`void`
`1060`	`1072`	`_PyInterpreterState_SetNotRunningMain(PyInterpreterState *interp)`
`1061`	`1073`	`{`
`1062`		`- assert(interp->threads.main == current_fast_get());`
`1063`		`- interp->threads.main = NULL;`
	`1074`	`+ assert(get_main_thread(interp) == current_fast_get());`
	`1075`	`+ set_main_thread(interp, NULL);`
`1064`	`1076`	`}`
`1065`	`1077`
`1066`	`1078`	`int`
`1067`	`1079`	`_PyInterpreterState_IsRunningMain(PyInterpreterState *interp)`
`1068`	`1080`	`{`
`1069`		`- if (interp->threads.main != NULL) {`
	`1081`	`+ if (get_main_thread(interp) != NULL) {`
`1070`	`1082`	`return 1;`
`1071`	`1083`	`}`
`1072`	`1084`	`// Embedders might not know to call _PyInterpreterState_SetRunningMain(),`
`@@ -1082,18 +1094,15 @@ int`
`1082`	`1094`	`_PyThreadState_IsRunningMain(PyThreadState *tstate)`
`1083`	`1095`	`{`
`1084`	`1096`	`PyInterpreterState *interp = tstate->interp;`
`1085`		`- if (interp->threads.main != NULL) {`
`1086`		`- return tstate == interp->threads.main;`
`1087`		`- }`
`1088`	`1097`	`// See the note in _PyInterpreterState_IsRunningMain() about`
`1089`	`1098`	`// possible false negatives here for embedders.`
`1090`		`- return 0;`
	`1099`	`+ return get_main_thread(interp) == tstate;`
`1091`	`1100`	`}`
`1092`	`1101`
`1093`	`1102`	`int`
`1094`	`1103`	`_PyInterpreterState_FailIfRunningMain(PyInterpreterState *interp)`
`1095`	`1104`	`{`
`1096`		`- if (interp->threads.main != NULL) {`
	`1105`	`+ if (get_main_thread(interp) != NULL) {`
`1097`	`1106`	`PyErr_SetString(PyExc_InterpreterError,`
`1098`	`1107`	`"interpreter already running");`
`1099`	`1108`	`return -1;`
`@@ -1105,8 +1114,8 @@ void`
`1105`	`1114`	`_PyInterpreterState_ReinitRunningMain(PyThreadState *tstate)`
`1106`	`1115`	`{`
`1107`	`1116`	`PyInterpreterState *interp = tstate->interp;`
`1108`		`- if (interp->threads.main != tstate) {`
`1109`		`- interp->threads.main = NULL;`
	`1117`	`+ if (get_main_thread(interp) != tstate) {`
	`1118`	`+ set_main_thread(interp, NULL);`
`1110`	`1119`	`}`
`1111`	`1120`	`}`
`1112`	`1121`