Nov 9, 2022 · Nov 9, 2022 · Nov 9, 2022 · Nov 9, 2022
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-11-09-16-02-27.gh-issue-99293.oPstNV.rst b/Misc/NEWS.d/next/Core and Builtins/2022-11-09-16-02-27.gh-issue-99293.oPstNV.rst
 Fix an issue where extension modules could inadvertently trigger an assertion error in typeobject.c by clearing the Py_TPFLAGS_VALID_VERSION_TAG tp_flag without clearing the tp_version_tag field. (Extension modules should use PyType_Modified() instead, however.)
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
    unsigned int h = MCACHE_HASH_METHOD(type, name);
    struct type_cache *cache = get_type_cache();
    struct type_cache_entry *entry = &cache->hashtable[h];
    /* Some extension modules (e.g. those generated by SWIG) don't always
     * change/clear tp_version_tag when they clear the
     * Py_TPFLAGS_VALID_VERSION_TAG tp_flag, so check both tp_version_tag
     * and the tp_flag. (Invalidated cache entries are replaced below.)
     */
    if (entry->version == type->tp_version_tag &&
        entry->name == name) {
        entry->name == name &&
        _PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
 #if MCACHE_STATS
        cache->hits++;
 #endif
        assert(_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG));
        return entry->value;
    }
Original file line number	Diff line number	Diff line change
Expand Up		@@ -4176,12 +4176,17 @@ _PyType_Lookup(PyTypeObject type, PyObject name)
		unsigned int h = MCACHE_HASH_METHOD(type, name);
		struct type_cache *cache = get_type_cache();
		struct type_cache_entry *entry = &cache->hashtable[h];
		/* Some extension modules (e.g. those generated by SWIG) don't always
		* change/clear tp_version_tag when they clear the
		* Py_TPFLAGS_VALID_VERSION_TAG tp_flag, so check both tp_version_tag
		* and the tp_flag. (Invalidated cache entries are replaced below.)
		*/
		if (entry->version == type->tp_version_tag &&
		entry->name == name) {
		entry->name == name &&
		_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
		#if MCACHE_STATS
		cache->hits++;
		#endif
		assert(_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG));
		return entry->value;
		}

Copy link Member Fidget-SpinnerNov 9, 2022• edited Loading Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. For other reviewers wondering what happens down this code path if`Py_TPFLAGS_VALID_VERSION_TAG` is not set: A normal lookup happens where we walk the MRO. We assign a new version tag to the type. This sets`Py_TPFLAGS_VALID_VERSION_TAG`. So this should be safe.
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