gh-102381: don't call watcher callback with dead object (#102382)

Co-authored-by: T. Wouters <thomas@python.org>

4 files changed, 31 insertions, 20 deletions

diff --git a/Include/cpython/code.h b/Include/cpython/code.h
index 0e4bd8a..abcf125 100644
--- a/Include/cpython/code.h
+++ b/Include/cpython/code.h
@@ -224,9 +224,14 @@ PyAPI_FUNC(int) PyCode_Addr2Line(PyCodeObject *, int);
 
 PyAPI_FUNC(int) PyCode_Addr2Location(PyCodeObject *, int, int *, int *, int *, int *);
 
-typedef enum PyCodeEvent {
-  PY_CODE_EVENT_CREATE,
-  PY_CODE_EVENT_DESTROY
+#define PY_FOREACH_CODE_EVENT(V) \
+    V(CREATE)                 \
+    V(DESTROY)
+
+typedef enum {
+    #define PY_DEF_EVENT(op) PY_CODE_EVENT_##op,
+    PY_FOREACH_CODE_EVENT(PY_DEF_EVENT)
+    #undef PY_DEF_EVENT
 } PyCodeEvent;
 
 
@@ -236,7 +241,7 @@ typedef enum PyCodeEvent {
  * The callback is invoked with a borrowed reference to co, after it is
  * created and before it is destroyed.
  *
- * If the callback returns with an exception set, it must return -1. Otherwise
+ * If the callback sets an exception, it must return -1. Otherwise
  * it should return 0.
  */
 typedef int (*PyCode_WatchCallback)(
diff --git a/Include/cpython/dictobject.h b/Include/cpython/dictobject.h
index 5001f35..ddada92 100644
--- a/Include/cpython/dictobject.h
+++ b/Include/cpython/dictobject.h
@@ -16,11 +16,11 @@ typedef struct {
 
     /* Dictionary version: globally unique, value change each time
        the dictionary is modified */
-#ifdef Py_BUILD_CORE       
+#ifdef Py_BUILD_CORE
     uint64_t ma_version_tag;
 #else
     Py_DEPRECATED(3.12) uint64_t ma_version_tag;
-#endif        
+#endif
 
     PyDictKeysObject *ma_keys;
 
@@ -90,13 +90,18 @@ PyAPI_FUNC(PyObject *) _PyDictView_Intersect(PyObject* self, PyObject *other);
 
 /* Dictionary watchers */
 
+#define PY_FOREACH_DICT_EVENT(V) \
+    V(ADDED)                     \
+    V(MODIFIED)                  \
+    V(DELETED)                   \
+    V(CLONED)                    \
+    V(CLEARED)                   \
+    V(DEALLOCATED)
+
 typedef enum {
-    PyDict_EVENT_ADDED,
-    PyDict_EVENT_MODIFIED,
-    PyDict_EVENT_DELETED,
-    PyDict_EVENT_CLONED,
-    PyDict_EVENT_CLEARED,
-    PyDict_EVENT_DEALLOCATED,
+    #define PY_DEF_EVENT(EVENT) PyDict_EVENT_##EVENT,
+    PY_FOREACH_DICT_EVENT(PY_DEF_EVENT)
+    #undef PY_DEF_EVENT
 } PyDict_WatchEvent;
 
 // Callback to be invoked when a watched dict is cleared, dealloced, or modified.
diff --git a/Include/cpython/funcobject.h b/Include/cpython/funcobject.h
index 5979feb..c716330 100644
--- a/Include/cpython/funcobject.h
+++ b/Include/cpython/funcobject.h
@@ -131,17 +131,17 @@ PyAPI_DATA(PyTypeObject) PyStaticMethod_Type;
 PyAPI_FUNC(PyObject *) PyClassMethod_New(PyObject *);
 PyAPI_FUNC(PyObject *) PyStaticMethod_New(PyObject *);
 
-#define FOREACH_FUNC_EVENT(V) \
-    V(CREATE)                 \
-    V(DESTROY)                \
-    V(MODIFY_CODE)            \
-    V(MODIFY_DEFAULTS)        \
+#define PY_FOREACH_FUNC_EVENT(V) \
+    V(CREATE)                    \
+    V(DESTROY)                   \
+    V(MODIFY_CODE)               \
+    V(MODIFY_DEFAULTS)           \
     V(MODIFY_KWDEFAULTS)
 
 typedef enum {
-    #define DEF_EVENT(EVENT) PyFunction_EVENT_##EVENT,
-    FOREACH_FUNC_EVENT(DEF_EVENT)
-    #undef DEF_EVENT
+    #define PY_DEF_EVENT(EVENT) PyFunction_EVENT_##EVENT,
+    PY_FOREACH_FUNC_EVENT(PY_DEF_EVENT)
+    #undef PY_DEF_EVENT
 } PyFunction_WatchEvent;
 
 /*
diff --git a/Include/internal/pycore_dict.h b/Include/internal/pycore_dict.h
index c74a343..1af5e59 100644
--- a/Include/internal/pycore_dict.h
+++ b/Include/internal/pycore_dict.h
@@ -164,6 +164,7 @@ _PyDict_NotifyEvent(PyDict_WatchEvent event,
                     PyObject *key,
                     PyObject *value)
 {
+    assert(Py_REFCNT((PyObject*)mp) > 0);
     int watcher_bits = mp->ma_version_tag & DICT_VERSION_MASK;
     if (watcher_bits) {
         _PyDict_SendEvent(watcher_bits, event, mp, key, value);