Handle race when clearing side exits of side exits

markshannon · markshannon · commit 25a889a146f4 · 2024-04-30T11:25:29.000+01:00
diff --git a/Python/optimizer.c b/Python/optimizer.c
@@ -82,10 +82,12 @@ get_index_for_executor(PyCodeObject *code, _Py_CODEUNIT *instr)
 static void
 insert_executor(PyCodeObject *code, _Py_CODEUNIT *instr, int index, _PyExecutorObject *executor)
 {
+    _PyExecutorObject *old_executor = NULL;
     Py_INCREF(executor);
     if (instr->op.code == ENTER_EXECUTOR) {
         assert(index == instr->op.arg);
-        _Py_ExecutorClear(code->co_executors->executors[index]);
+        old_executor = code->co_executors->executors[index];
+        code->co_executors->executors[index] = NULL;
     }
     else {
         assert(code->co_executors->size == index);
@@ -100,6 +102,7 @@ insert_executor(PyCodeObject *code, _Py_CODEUNIT *instr, int index, _PyExecutorO
     assert(index < MAX_EXECUTORS_SIZE);
     instr->op.code = ENTER_EXECUTOR;
     instr->op.arg = index;
+    Py_XDECREF(old_executor);
 }
 
 int
@@ -1591,13 +1594,14 @@ _Py_ExecutorClear(_PyExecutorObject *executor)
         executor->exits[i].temperature = initial_unreachable_backoff_counter();
     }
     _Py_CODEUNIT *instruction = &_PyCode_CODE(code)[executor->vm_data.index];
-    assert(instruction->op.code == ENTER_EXECUTOR);
-    int index = instruction->op.arg;
-    assert(code->co_executors->executors[index] == executor);
-    instruction->op.code = executor->vm_data.opcode;
-    instruction->op.arg = executor->vm_data.oparg;
-    executor->vm_data.code = NULL;
-    Py_CLEAR(code->co_executors->executors[index]);
+    if (instruction->op.code == ENTER_EXECUTOR) {
+        int index = instruction->op.arg;
+        assert(code->co_executors->executors[index] == executor);
+        instruction->op.code = executor->vm_data.opcode;
+        instruction->op.arg = executor->vm_data.oparg;
+        executor->vm_data.code = NULL;
+        Py_CLEAR(code->co_executors->executors[index]);
+    }
 }
 
 void
