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[3.13] GH-119462: Enforce invariants of type versioning. Backport of GH-120731. (#120748) 

* Remove uses of Py_TPFLAGS_VALID_VERSION_TAG
This commit is contained in:
Mark Shannon 2024-06-20 15:09:32 +01:00 committed by GitHub
parent d0a5e40f01
commit b8fd80f91b
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GPG Key ID: B5690EEEBB952194
7 changed files with 68 additions and 86 deletions
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4
Doc/c-api/typeobj.rst
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@ -1328,8 +1328,8 @@ and :c:data:`PyType_Type` effectively act as defaults.)
To indicate that a class has changed call :c:func:`PyType_Modified`
.. warning::
This flag is present in header files, but is an internal feature and should
not be used. It will be removed in a future version of CPython
This flag is present in header files, but is not be used.
It will be removed in a future version of CPython
.. c:member:: const char* PyTypeObject.tp_doc

2
Include/object.h
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@ -703,7 +703,7 @@ given type object has a specified feature.
/* Objects behave like an unbound method */
#define Py_TPFLAGS_METHOD_DESCRIPTOR (1UL << 17)
/* Object has up-to-date type attribute cache */
/* Unused. Legacy flag */
#define Py_TPFLAGS_VALID_VERSION_TAG (1UL << 19)
/* Type is abstract and cannot be instantiated */

29
Lib/test/test_type_cache.py
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@ -92,6 +92,21 @@ class TypeCacheTests(unittest.TestCase):
new_version = type_get_version(C)
self.assertEqual(new_version, 0)
def test_119462(self):
class Holder:
value = None
@classmethod
def set_value(cls):
cls.value = object()
class HolderSub(Holder):
pass
for _ in range(1050):
Holder.set_value()
HolderSub.value
@support.cpython_only
@requires_specialization
@ -105,8 +120,10 @@ class TypeCacheWithSpecializationTests(unittest.TestCase):
if type_get_version(type_) == 0:
self.skipTest("Could not assign valid type version")
def _assign_and_check_version_0(self, user_type):
def _no_more_versions(self, user_type):
type_modified(user_type)
for _ in range(1001):
type_assign_specific_version_unsafe(user_type, 1000_000_000)
type_assign_specific_version_unsafe(user_type, 0)
self.assertEqual(type_get_version(user_type), 0)
@ -135,7 +152,7 @@ class TypeCacheWithSpecializationTests(unittest.TestCase):
self._check_specialization(load_foo_1, A, "LOAD_ATTR", should_specialize=True)
del load_foo_1
self._assign_and_check_version_0(A)
self._no_more_versions(A)
def load_foo_2(type_):
return type_.foo
@ -186,7 +203,7 @@ class TypeCacheWithSpecializationTests(unittest.TestCase):
self._check_specialization(load_x_1, G(), "LOAD_ATTR", should_specialize=True)
del load_x_1
self._assign_and_check_version_0(G)
self._no_more_versions(G)
def load_x_2(instance):
instance.x
@ -205,7 +222,7 @@ class TypeCacheWithSpecializationTests(unittest.TestCase):
self._check_specialization(store_bar_1, B(), "STORE_ATTR", should_specialize=True)
del store_bar_1
self._assign_and_check_version_0(B)
self._no_more_versions(B)
def store_bar_2(type_):
type_.bar = 10
@ -225,7 +242,7 @@ class TypeCacheWithSpecializationTests(unittest.TestCase):
self._check_specialization(call_class_1, F, "CALL", should_specialize=True)
del call_class_1
self._assign_and_check_version_0(F)
self._no_more_versions(F)
def call_class_2(type_):
type_()
@ -244,7 +261,7 @@ class TypeCacheWithSpecializationTests(unittest.TestCase):
self._check_specialization(to_bool_1, H(), "TO_BOOL", should_specialize=True)
del to_bool_1
self._assign_and_check_version_0(H)
self._no_more_versions(H)
def to_bool_2(instance):
not instance

4
Misc/NEWS.d/next/Core and Builtins/2024-06-19-11-10-50.gh-issue-119462.DpcqSe.rst Normal file
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@ -0,0 +1,4 @@
Make sure that invariants of type versioning are maintained:
* Superclasses always have their version number assigned before subclasses
* The version tag is always zero if the tag is not valid.
* The version tag is always non-zero if the tag is valid.

2
Modules/_testcapimodule.c
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@ -2415,7 +2415,7 @@ type_assign_specific_version_unsafe(PyObject *self, PyObject *args)
}
assert(!PyType_HasFeature(type, Py_TPFLAGS_IMMUTABLETYPE));
type->tp_version_tag = version;
type->tp_flags |= Py_TPFLAGS_VALID_VERSION_TAG;
type->tp_versions_used++;
Py_RETURN_NONE;
}

2
Modules/pyexpat.c
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@ -1651,7 +1651,7 @@ PyDoc_STRVAR(pyexpat_module_documentation,
static int init_handler_descrs(pyexpat_state *state)
{
int i;
assert(!PyType_HasFeature(state->xml_parse_type, Py_TPFLAGS_VALID_VERSION_TAG));
assert(state->xml_parse_type->tp_version_tag == 0);
for (i = 0; handler_info[i].name != NULL; i++) {
struct HandlerInfo *hi = &handler_info[i];
hi->getset.name = hi->name;

111
Objects/typeobject.c
View File

@ -973,43 +973,21 @@ PyType_Unwatch(int watcher_id, PyObject* obj)
return 0;
}
#ifdef Py_GIL_DISABLED
static void
type_modification_starting_unlocked(PyTypeObject *type)
set_version_unlocked(PyTypeObject *tp, unsigned int version)
{
ASSERT_TYPE_LOCK_HELD();
/* Clear version tags on all types, but leave the valid
version tag intact. This prepares for a modification so that
any concurrent readers of the type cache will not see invalid
values.
*/
if (!_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
return;
#ifndef Py_GIL_DISABLED
if (version) {
tp->tp_versions_used++;
}
PyObject *subclasses = lookup_tp_subclasses(type);
if (subclasses != NULL) {
assert(PyDict_CheckExact(subclasses));
Py_ssize_t i = 0;
PyObject *ref;
while (PyDict_Next(subclasses, &i, NULL, &ref)) {
PyTypeObject *subclass = type_from_ref(ref);
if (subclass == NULL) {
continue;
#else
if (version) {
_Py_atomic_add_uint16(&tp->tp_versions_used, 1);
}
type_modification_starting_unlocked(subclass);
Py_DECREF(subclass);
}
}
/* 0 is not a valid version tag */
_Py_atomic_store_uint32_release(&type->tp_version_tag, 0);
}
#endif
FT_ATOMIC_STORE_UINT32_RELAXED(tp->tp_version_tag, version);
}
static void
type_modified_unlocked(PyTypeObject *type)
@ -1020,16 +998,16 @@ type_modified_unlocked(PyTypeObject *type)
Invariants:
- before Py_TPFLAGS_VALID_VERSION_TAG can be set on a type,
- before tp_version_tag can be set on a type,
it must first be set on all super types.
This function clears the Py_TPFLAGS_VALID_VERSION_TAG of a
This function clears the tp_version_tag of a
type (so it must first clear it on all subclasses). The
tp_version_tag value is meaningless unless this flag is set.
tp_version_tag value is meaningless when equal to zero.
We don't assign new version tags eagerly, but only as
needed.
*/
if (!_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
if (type->tp_version_tag == 0) {
return;
}
@ -1069,8 +1047,7 @@ type_modified_unlocked(PyTypeObject *type)
}
}
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
FT_ATOMIC_STORE_UINT32_RELAXED(type->tp_version_tag, 0); /* 0 is not a valid version tag */
set_version_unlocked(type, 0); /* 0 is not a valid version tag */
if (PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
// This field *must* be invalidated if the type is modified (see the
// comment on struct _specialization_cache):
@ -1082,7 +1059,7 @@ void
PyType_Modified(PyTypeObject *type)
{
// Quick check without the lock held
if (!_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
if (type->tp_version_tag == 0) {
return;
}
@ -1146,8 +1123,7 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {
clear:
assert(!(type->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN));
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
FT_ATOMIC_STORE_UINT32_RELAXED(type->tp_version_tag, 0); /* 0 is not a valid version tag */
set_version_unlocked(type, 0); /* 0 is not a valid version tag */
if (PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
// This field *must* be invalidated if the type is modified (see the
// comment on struct _specialization_cache):
@ -1162,12 +1138,11 @@ assign_version_tag(PyInterpreterState *interp, PyTypeObject *type)
{
ASSERT_TYPE_LOCK_HELD();
/* Ensure that the tp_version_tag is valid and set
Py_TPFLAGS_VALID_VERSION_TAG. To respect the invariant, this
must first be done on all super classes. Return 0 if this
cannot be done, 1 if Py_TPFLAGS_VALID_VERSION_TAG.
/* Ensure that the tp_version_tag is valid.
* To respect the invariant, this must first be done on all super classes.
* Return 0 if this cannot be done, 1 if tp_version_tag is set.
*/
if (_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
if (type->tp_version_tag != 0) {
return 1;
}
if (!_PyType_HasFeature(type, Py_TPFLAGS_READY)) {
@ -1176,15 +1151,22 @@ assign_version_tag(PyInterpreterState *interp, PyTypeObject *type)
if (type->tp_versions_used >= MAX_VERSIONS_PER_CLASS) {
return 0;
}
type->tp_versions_used++;
PyObject *bases = lookup_tp_bases(type);
Py_ssize_t n = PyTuple_GET_SIZE(bases);
for (Py_ssize_t i = 0; i < n; i++) {
PyObject *b = PyTuple_GET_ITEM(bases, i);
if (!assign_version_tag(interp, _PyType_CAST(b))) {
return 0;
}
}
if (type->tp_flags & Py_TPFLAGS_IMMUTABLETYPE) {
/* static types */
if (NEXT_GLOBAL_VERSION_TAG > _Py_MAX_GLOBAL_TYPE_VERSION_TAG) {
/* We have run out of version numbers */
return 0;
}
FT_ATOMIC_STORE_UINT32_RELAXED(type->tp_version_tag,
NEXT_GLOBAL_VERSION_TAG++);
set_version_unlocked(type, NEXT_GLOBAL_VERSION_TAG++);
assert (type->tp_version_tag <= _Py_MAX_GLOBAL_TYPE_VERSION_TAG);
}
else {
@ -1193,19 +1175,9 @@ assign_version_tag(PyInterpreterState *interp, PyTypeObject *type)
/* We have run out of version numbers */
return 0;
}
FT_ATOMIC_STORE_UINT32_RELAXED(type->tp_version_tag,
NEXT_VERSION_TAG(interp)++);
set_version_unlocked(type, NEXT_VERSION_TAG(interp)++);
assert (type->tp_version_tag != 0);
}
PyObject *bases = lookup_tp_bases(type);
Py_ssize_t n = PyTuple_GET_SIZE(bases);
for (Py_ssize_t i = 0; i < n; i++) {
PyObject *b = PyTuple_GET_ITEM(bases, i);
if (!assign_version_tag(interp, _PyType_CAST(b)))
return 0;
}
type->tp_flags |= Py_TPFLAGS_VALID_VERSION_TAG;
return 1;
}
@ -3126,7 +3098,7 @@ mro_internal_unlocked(PyTypeObject *type, int initial, PyObject **p_old_mro)
else {
/* For static builtin types, this is only called during init
before the method cache has been populated. */
assert(_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG));
assert(type->tp_version_tag);
}
if (p_old_mro != NULL)
@ -5275,7 +5247,7 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
#else
if (entry->version == type->tp_version_tag &&
entry->name == name) {
assert(_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG));
assert(type->tp_version_tag);
OBJECT_STAT_INC_COND(type_cache_hits, !is_dunder_name(name));
OBJECT_STAT_INC_COND(type_cache_dunder_hits, is_dunder_name(name));
Py_XINCREF(entry->value);
@ -5298,7 +5270,6 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
if (MCACHE_CACHEABLE_NAME(name)) {
has_version = assign_version_tag(interp, type);
version = type->tp_version_tag;
assert(!has_version || _PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG));
}
END_TYPE_LOCK()
@ -5582,16 +5553,6 @@ type_setattro(PyObject *self, PyObject *name, PyObject *value)
return -1;
}
#ifdef Py_GIL_DISABLED
// In free-threaded builds readers can race with the lock-free portion
// of the type cache and the assignment into the dict. We clear all of the
// versions initially so no readers will succeed in the lock-free case.
// They'll then block on the type lock until the update below is done.
type_modification_starting_unlocked(type);
#endif
res = _PyDict_SetItem_LockHeld((PyDictObject *)dict, name, value);
/* Clear the VALID_VERSION flag of 'type' and all its
subclasses. This could possibly be unified with the
update_subclasses() recursion in update_slot(), but carefully:
@ -5599,6 +5560,8 @@ type_setattro(PyObject *self, PyObject *name, PyObject *value)
recursing into subclasses. */
type_modified_unlocked(type);
res = _PyDict_SetItem_LockHeld((PyDictObject *)dict, name, value);
if (res == 0) {
if (is_dunder_name(name)) {
res = update_slot(type, name);
@ -5710,7 +5673,6 @@ fini_static_type(PyInterpreterState *interp, PyTypeObject *type,
if (final) {
type->tp_flags &= ~Py_TPFLAGS_READY;
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
type->tp_version_tag = 0;
}
@ -8329,12 +8291,11 @@ init_static_type(PyInterpreterState *interp, PyTypeObject *self,
assert(NEXT_GLOBAL_VERSION_TAG <= _Py_MAX_GLOBAL_TYPE_VERSION_TAG);
self->tp_version_tag = NEXT_GLOBAL_VERSION_TAG++;
self->tp_flags |= Py_TPFLAGS_VALID_VERSION_TAG;
}
else {
assert(!initial);
assert(self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN);
assert(self->tp_flags & Py_TPFLAGS_VALID_VERSION_TAG);
assert(self->tp_version_tag != 0);
}
managed_static_type_state_init(interp, self, isbuiltin, initial);