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GH-119462: Enforce invariants of type versioning (GH-120731)

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* Remove uses of Py_TPFLAGS_VALID_VERSION_TAG
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Mark Shannon 2024-06-19 17:38:45 +01:00 • committed by GitHub
parent f385d99f57
commit 00257c746c
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7 changed files with 87 additions and 103 deletions
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148
Objects/typeobject.c
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@ -974,43 +974,37 @@ 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
PyInterpreterState *interp = _PyInterpreterState_GET();
// lookup the old version and set to null
if (tp->tp_version_tag != 0) {
PyTypeObject **slot =
interp->types.type_version_cache
+ (tp->tp_version_tag % TYPE_VERSION_CACHE_SIZE);
*slot = NULL;
}
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;
}
type_modification_starting_unlocked(subclass);
Py_DECREF(subclass);
}
if (version) {
tp->tp_versions_used++;
}
#else
if (version) {
_Py_atomic_add_uint16(&tp->tp_versions_used, 1);
}
/* 0 is not a valid version tag */
_PyType_SetVersion(type, 0);
}
#endif
FT_ATOMIC_STORE_UINT32_RELAXED(tp->tp_version_tag, version);
#ifndef Py_GIL_DISABLED
if (version != 0) {
PyTypeObject **slot =
interp->types.type_version_cache
+ (version % TYPE_VERSION_CACHE_SIZE);
*slot = tp;
}
#endif
}
static void
type_modified_unlocked(PyTypeObject *type)
@ -1021,16 +1015,16 @@ 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;
}
@ -1070,8 +1064,7 @@ type_modified_unlocked(PyTypeObject *type)
}
}
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
_PyType_SetVersion(type, 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):
@ -1083,7 +1076,7 @@ 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;
}
@ -1147,8 +1140,7 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {
clear:
assert(!(type->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN));
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
_PyType_SetVersion(type, 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):
@ -1168,25 +1160,10 @@ This is similar to func_version_cache.
void
_PyType_SetVersion(PyTypeObject *tp, unsigned int version)
{
#ifndef Py_GIL_DISABLED
PyInterpreterState *interp = _PyInterpreterState_GET();
// lookup the old version and set to null
if (tp->tp_version_tag != 0) {
PyTypeObject **slot =
interp->types.type_version_cache
+ (tp->tp_version_tag % TYPE_VERSION_CACHE_SIZE);
*slot = NULL;
}
#endif
FT_ATOMIC_STORE_UINT32_RELAXED(tp->tp_version_tag, version);
#ifndef Py_GIL_DISABLED
if (version != 0) {
PyTypeObject **slot =
interp->types.type_version_cache
+ (version % TYPE_VERSION_CACHE_SIZE);
*slot = tp;
}
#endif
BEGIN_TYPE_LOCK()
set_version_unlocked(tp, version);
END_TYPE_LOCK()
}
PyTypeObject *
@ -1221,12 +1198,11 @@ 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)) {
@ -1235,14 +1211,22 @@ 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;
}
_PyType_SetVersion(type, NEXT_GLOBAL_VERSION_TAG++);
set_version_unlocked(type, NEXT_GLOBAL_VERSION_TAG++);
assert (type->tp_version_tag <= _Py_MAX_GLOBAL_TYPE_VERSION_TAG);
}
else {
@ -1251,18 +1235,9 @@ assign_version_tag(PyInterpreterState *interp, PyTypeObject *type)
/* We have run out of version numbers */
return 0;
}
_PyType_SetVersion(type, 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;
}
@ -3318,7 +3293,7 @@ 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)
@ -5463,7 +5438,7 @@ _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);
@ -5486,7 +5461,6 @@ _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()
@ -5770,16 +5744,6 @@ 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:
@ -5787,6 +5751,8 @@ 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);
@ -5898,7 +5864,6 @@ fini_static_type(PyInterpreterState *interp, PyTypeObject *type,
if (final) {
type->tp_flags &= ~Py_TPFLAGS_READY;
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
_PyType_SetVersion(type, 0);
}
@ -8516,12 +8481,11 @@ init_static_type(PyInterpreterState *interp, PyTypeObject *self,
assert(NEXT_GLOBAL_VERSION_TAG <= _Py_MAX_GLOBAL_TYPE_VERSION_TAG);
_PyType_SetVersion(self, 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);