From 50cf12b2e9d73d20723ef7fbc0d5aad27edbbfb0 Mon Sep 17 00:00:00 2001
From: Matt Page <mpage@meta.com>
Date: Thu, 9 May 2024 12:17:15 -0700
Subject: [PATCH 1/3] Fix data races reported by TSAN on `interp->threads.main`

Use relaxed loads/stores when reading/writing to this field.

This fixes races like https://gist.github.com/mpage/e07497ad8dd444a789ff306cb7996acc
---
 Python/pystate.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/Python/pystate.c b/Python/pystate.c
index b1e085bb806915..de6a768a50f997 100644
--- 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);
     }
 }
 

From f412a0cdd96bdca224168ee902098aa837495355 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Thu, 9 May 2024 19:47:14 +0000
Subject: [PATCH 2/3] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../2024-05-09-19-47-12.gh-issue-117657.Vn0Yey.rst               | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2024-05-09-19-47-12.gh-issue-117657.Vn0Yey.rst

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
new file mode 100644
index 00000000000000..db4c5813ca610c
--- /dev/null
+++ 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.

From 17d86222d81259cb903776869640c83d3d3eeed9 Mon Sep 17 00:00:00 2001
From: Matt Page <mpage@meta.com>
Date: Thu, 9 May 2024 15:03:46 -0700
Subject: [PATCH 3/3] Remove corresponding suppressions

---
 Tools/tsan/suppressions_free_threading.txt | 2 --
 1 file changed, 2 deletions(-)

diff --git a/Tools/tsan/suppressions_free_threading.txt b/Tools/tsan/suppressions_free_threading.txt
index 7f91a9113c4e1a..d5f4cd7acd36b7 100644
--- 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