From 837645e31166e141149cc7a984ab832ac73d4896 Mon Sep 17 00:00:00 2001
From: Matt Page <mpage@meta.com>
Date: Tue, 10 Sep 2024 16:53:29 -0700
Subject: [PATCH] Fix data race in _PyInstruction_GetLength

Read the opcode atomically, the interpreter may be specializing it
---
 Python/instrumentation.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Python/instrumentation.c b/Python/instrumentation.c
index 9a7cc027553f4f..18b77193fc4c52 100644
--- a/Python/instrumentation.c
+++ b/Python/instrumentation.c
@@ -327,7 +327,8 @@ _PyInstruction_GetLength(PyCodeObject *code, int offset)
 {
     ASSERT_WORLD_STOPPED_OR_LOCKED(code);
 
-    int opcode = _PyCode_CODE(code)[offset].op.code;
+    int opcode =
+        FT_ATOMIC_LOAD_UINT8_RELAXED(_PyCode_CODE(code)[offset].op.code);
     assert(opcode != 0);
     assert(opcode != RESERVED);
     if (opcode == INSTRUMENTED_LINE) {