gh-154701: prevent executor self-links in JIT cold exits (GH-155323)

* prevent executor self-links in JIT cold exits

* 📜🤖 Added by blurb_it.

* fix windows ci

---------
(cherry picked from commit 716cbae)

Co-authored-by: Hai Zhu <haiizhu@outlook.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Author: 2 people

Include/internal/pycore_optimizer.h

@@ -206,7 +206,7 @@ typedef struct _PyExecutorObject {
 PyAPI_FUNC(_PyExecutorObject*) _Py_GetExecutor(PyCodeObject *code, int offset);
 
 int _Py_ExecutorInit(_PyExecutorObject *, const _PyBloomFilter *);
-void _Py_ExecutorDetach(_PyExecutorObject *);
+PyAPI_FUNC(void) _Py_ExecutorDetach(_PyExecutorObject *);
 PyAPI_FUNC(void) _Py_Executor_DependsOn(_PyExecutorObject *executor, void *obj);
 
 /* We use a bloomfilter with k = 6, m = 256

Include/internal/pycore_uop_metadata.h

@@ -11,7 +11,7 @@
 
 from test.support import (script_helper, requires_specialization,
                           import_helper, Py_GIL_DISABLED, requires_jit_enabled,
-                          reset_code)
+                          reset_code, SHORT_TIMEOUT, isolation)
 
 _testinternalcapi = import_helper.import_module("_testinternalcapi")
 
@@ -6200,6 +6200,28 @@ def __exit__(self, e, v, t): ...
                 f1()
         """), PYTHON_JIT="1")
 
+    @isolation.runInSubprocess(timeout=SHORT_TIMEOUT)
+    def test_for_iter_side_exit_does_not_self_link(self):
+        def exhaust(iterator):
+            for _ in iterator:
+                pass
+
+        values = range(TIER2_THRESHOLD)
+        # After the initial trace, MAX_CHAIN_DEPTH side exits cause the final
+        # executor to be installed at FOR_ITER.
+        warmup_iterators = (
+            iter(set(values)),
+            iter(dict.fromkeys(values)),
+            iter(values),
+            enumerate(values),
+            zip(values, values),
+        )
+        for iterator in warmup_iterators:
+            exhaust(iterator)
+
+        # A different iterator type must not link that executor to itself.
+        exhaust(map(bool, values))
+
 def global_identity(x):
     return x
 

Lib/test/test_capi/test_opt.py

@@ -0,0 +1 @@
+Fix an infinite loop in JIT when a ``FOR_ITER`` side exit links an executor back to itself.

Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-10-14-56.gh-issue-154701.zulh2S.rst

@@ -6308,6 +6308,10 @@ dummy_func(
             if (target->op.code == ENTER_EXECUTOR) {
                 PyCodeObject *code = _PyFrame_GetCode(frame);
                 executor = code->co_executors->executors[target->op.arg];
+                if (executor == _PyExecutor_FromExit(exit)) {
+                    _Py_ExecutorDetach(executor);
+                    GOTO_TIER_ONE(target);
+                }
                 Py_INCREF(executor);
                 assert(tstate->jit_exit == exit);
                 exit->executor = executor;