From 6a249584eb6f778bf76adf7179a1e1f53c193d3e Mon Sep 17 00:00:00 2001
From: Matt Page <mpage@meta.com>
Date: Mon, 18 Nov 2024 22:08:31 -0800
Subject: [PATCH] Stop the world around assignments to `tstate->eval_frame`

---
 Python/perf_trampoline.c | 14 +++++++++++---
 Python/pystate.c         |  2 ++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/Python/perf_trampoline.c b/Python/perf_trampoline.c
index f144f7d436fe68d..22921876d1654dc 100644
--- a/Python/perf_trampoline.c
+++ b/Python/perf_trampoline.c
@@ -471,6 +471,14 @@ _PyPerfTrampoline_SetCallbacks(_PyPerf_Callbacks *callbacks)
     return 0;
 }
 
+static void
+set_eval_frame(PyThreadState *tstate, _PyFrameEvalFunction eval_frame)
+{
+    _PyEval_StopTheWorld(tstate->interp);
+    tstate->interp->eval_frame = eval_frame;
+    _PyEval_StartTheWorld(tstate->interp);
+}
+
 int
 _PyPerfTrampoline_Init(int activate)
 {
@@ -484,11 +492,11 @@ _PyPerfTrampoline_Init(int activate)
         return -1;
     }
     if (!activate) {
-        tstate->interp->eval_frame = NULL;
+        set_eval_frame(tstate, NULL);
         perf_status = PERF_STATUS_NO_INIT;
     }
     else {
-        tstate->interp->eval_frame = py_trampoline_evaluator;
+        set_eval_frame(tstate, py_trampoline_evaluator);
         if (new_code_arena() < 0) {
             return -1;
         }
@@ -514,7 +522,7 @@ _PyPerfTrampoline_Fini(void)
     }
     PyThreadState *tstate = _PyThreadState_GET();
     if (tstate->interp->eval_frame == py_trampoline_evaluator) {
-        tstate->interp->eval_frame = NULL;
+        set_eval_frame(tstate, NULL);
     }
     if (perf_status == PERF_STATUS_OK) {
         trampoline_api.free_state(trampoline_api.state);
diff --git a/Python/pystate.c b/Python/pystate.c
index 24ee73c145cbccd..a2a356d8b61b64f 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -2842,7 +2842,9 @@ _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState *interp,
     }
 #endif
     RARE_EVENT_INC(set_eval_frame_func);
+    _PyEval_StopTheWorld(interp);
     interp->eval_frame = eval_frame;
+    _PyEval_StartTheWorld(interp);
 }