diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-04-09-14-18-33.gh-issue-148037.aP3CSX.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-09-14-18-33.gh-issue-148037.aP3CSX.rst
new file mode 100644
index 00000000000000..b0cef595129817
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-09-14-18-33.gh-issue-148037.aP3CSX.rst
@@ -0,0 +1 @@
+Remove critical section from :c:func:`!PyCode_Addr2Line` in free-threading.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index ad1116890e23ce..8f3dabd6d753a1 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -1008,14 +1008,18 @@ PyCode_NewEmpty(const char *filename, const char *funcname, int firstlineno)
  * source location tracking (co_lines/co_positions)
  ******************/
 
-static int
-_PyCode_Addr2Line(PyCodeObject *co, int addrq)
+int
+PyCode_Addr2Line(PyCodeObject *co, int addrq)
 {
     if (addrq < 0) {
         return co->co_firstlineno;
     }
-    if (co->_co_monitoring && co->_co_monitoring->lines) {
-        return _Py_Instrumentation_GetLine(co, addrq/sizeof(_Py_CODEUNIT));
+    _PyCoMonitoringData *data = _Py_atomic_load_ptr_acquire(&co->_co_monitoring);
+    if (data) {
+        _PyCoLineInstrumentationData *lines = _Py_atomic_load_ptr_acquire(&data->lines);
+        if (lines) {
+            return _Py_Instrumentation_GetLine(co, addrq/sizeof(_Py_CODEUNIT));
+        }
     }
     assert(addrq >= 0 && addrq < _PyCode_NBYTES(co));
     PyCodeAddressRange bounds;
@@ -1040,16 +1044,6 @@ _PyCode_SafeAddr2Line(PyCodeObject *co, int addrq)
     return _PyCode_CheckLineNumber(addrq, &bounds);
 }
 
-int
-PyCode_Addr2Line(PyCodeObject *co, int addrq)
-{
-    int lineno;
-    Py_BEGIN_CRITICAL_SECTION(co);
-    lineno = _PyCode_Addr2Line(co, addrq);
-    Py_END_CRITICAL_SECTION();
-    return lineno;
-}
-
 void
 _PyLineTable_InitAddressRange(const char *linetable, Py_ssize_t length, int firstlineno, PyCodeAddressRange *range)
 {
diff --git a/Python/instrumentation.c b/Python/instrumentation.c
index 1aed6769d217fe..3990e318f427de 100644
--- a/Python/instrumentation.c
+++ b/Python/instrumentation.c
@@ -1511,11 +1511,9 @@ initialize_tools(PyCodeObject *code)
 }
 
 static void
-initialize_lines(PyCodeObject *code, int bytes_per_entry)
+initialize_lines(_PyCoLineInstrumentationData *line_data, PyCodeObject *code, int bytes_per_entry)
 {
     ASSERT_WORLD_STOPPED_OR_LOCKED(code);
-    _PyCoLineInstrumentationData *line_data = code->_co_monitoring->lines;
-
     assert(line_data != NULL);
     line_data->bytes_per_entry = bytes_per_entry;
     int code_len = (int)Py_SIZE(code);
@@ -1656,18 +1654,19 @@ allocate_instrumentation_data(PyCodeObject *code)
     ASSERT_WORLD_STOPPED_OR_LOCKED(code);
 
     if (code->_co_monitoring == NULL) {
-        code->_co_monitoring = PyMem_Malloc(sizeof(_PyCoMonitoringData));
-        if (code->_co_monitoring == NULL) {
+        _PyCoMonitoringData *monitoring = PyMem_Malloc(sizeof(_PyCoMonitoringData));
+        if (monitoring == NULL) {
             PyErr_NoMemory();
             return -1;
         }
-        code->_co_monitoring->local_monitors = (_Py_LocalMonitors){ 0 };
-        code->_co_monitoring->active_monitors = (_Py_LocalMonitors){ 0 };
-        code->_co_monitoring->tools = NULL;
-        code->_co_monitoring->lines = NULL;
-        code->_co_monitoring->line_tools = NULL;
-        code->_co_monitoring->per_instruction_opcodes = NULL;
-        code->_co_monitoring->per_instruction_tools = NULL;
+        monitoring->local_monitors = (_Py_LocalMonitors){ 0 };
+        monitoring->active_monitors = (_Py_LocalMonitors){ 0 };
+        monitoring->tools = NULL;
+        monitoring->lines = NULL;
+        monitoring->line_tools = NULL;
+        monitoring->per_instruction_opcodes = NULL;
+        monitoring->per_instruction_tools = NULL;
+        _Py_atomic_store_ptr_release(&code->_co_monitoring, monitoring);
     }
     return 0;
 }
@@ -1732,12 +1731,13 @@ update_instrumentation_data(PyCodeObject *code, PyInterpreterState *interp)
             else {
                 bytes_per_entry = 5;
             }
-            code->_co_monitoring->lines = PyMem_Malloc(1 + code_len * bytes_per_entry);
-            if (code->_co_monitoring->lines == NULL) {
+            _PyCoLineInstrumentationData *lines = PyMem_Malloc(1 + code_len * bytes_per_entry);
+            if (lines == NULL) {
                 PyErr_NoMemory();
                 return -1;
             }
-            initialize_lines(code, bytes_per_entry);
+            initialize_lines(lines, code, bytes_per_entry);
+            _Py_atomic_store_ptr_release(&code->_co_monitoring->lines, lines);
         }
         if (multitools && code->_co_monitoring->line_tools == NULL) {
             code->_co_monitoring->line_tools = PyMem_Malloc(code_len);