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GH-125174: Make immortal objects more robust, following design from PEP 683 (GH-125251)

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Mark Shannon 2024-10-10 18:19:08 +01:00 committed by GitHub
parent 01fc3b34cc
commit c9014374c5
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GPG Key ID: B5690EEEBB952194
17 changed files with 61 additions and 72 deletions
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2
Include/internal/pycore_global_objects_fini_generated.h generated
View File

@ -11,7 +11,7 @@ extern "C" {
#ifdef Py_DEBUG
static inline void
_PyStaticObject_CheckRefcnt(PyObject *obj) {
if (Py_REFCNT(obj) < _Py_IMMORTAL_REFCNT) {
if (!_Py_IsImmortal(obj)) {
fprintf(stderr, "Immortal Object has less refcnt than expected.\n");
_PyObject_Dump(obj);
}

34
Include/internal/pycore_object.h
View File

@ -16,9 +16,6 @@ extern "C" {
#include "pycore_pystate.h" // _PyInterpreterState_GET()
#include "pycore_uniqueid.h" // _PyType_IncrefSlow
#define _Py_IMMORTAL_REFCNT_LOOSE ((_Py_IMMORTAL_REFCNT >> 1) + 1)
// This value is added to `ob_ref_shared` for objects that use deferred
// reference counting so that they are not immediately deallocated when the
// non-deferred reference count drops to zero.
@ -27,25 +24,8 @@ extern "C" {
// `ob_ref_shared` are used for flags.
#define _Py_REF_DEFERRED (PY_SSIZE_T_MAX / 8)
// gh-121528, gh-118997: Similar to _Py_IsImmortal() but be more loose when
// comparing the reference count to stay compatible with C extensions built
// with the stable ABI 3.11 or older. Such extensions implement INCREF/DECREF
// as refcnt++ and refcnt-- without taking in account immortal objects. For
// example, the reference count of an immortal object can change from
// _Py_IMMORTAL_REFCNT to _Py_IMMORTAL_REFCNT+1 (INCREF) or
// _Py_IMMORTAL_REFCNT-1 (DECREF).
//
// This function should only be used in assertions. Otherwise, _Py_IsImmortal()
// must be used instead.
static inline int _Py_IsImmortalLoose(PyObject *op)
{
#if defined(Py_GIL_DISABLED)
return _Py_IsImmortal(op);
#else
return (op->ob_refcnt >= _Py_IMMORTAL_REFCNT_LOOSE);
#endif
}
#define _Py_IsImmortalLoose(op) _Py_IsImmortalLoose(_PyObject_CAST(op))
/* For backwards compatibility -- Do not use this */
#define _Py_IsImmortalLoose(op) _Py_IsImmortal
/* Check if an object is consistent. For example, ensure that the reference
@ -97,7 +77,7 @@ PyAPI_FUNC(int) _PyObject_IsFreed(PyObject *);
#else
#define _PyObject_HEAD_INIT(type) \
{ \
.ob_refcnt = _Py_IMMORTAL_REFCNT, \
.ob_refcnt = _Py_IMMORTAL_INITIAL_REFCNT, \
.ob_type = (type) \
}
#endif
@ -184,7 +164,7 @@ PyAPI_FUNC(void) _Py_SetImmortalUntracked(PyObject *op);
static inline void _Py_SetMortal(PyObject *op, Py_ssize_t refcnt)
{
if (op) {
assert(_Py_IsImmortalLoose(op));
assert(_Py_IsImmortal(op));
#ifdef Py_GIL_DISABLED
op->ob_tid = _Py_UNOWNED_TID;
op->ob_ref_local = 0;
@ -316,7 +296,7 @@ static inline void
_Py_INCREF_TYPE(PyTypeObject *type)
{
if (!_PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
assert(_Py_IsImmortalLoose(type));
assert(_Py_IsImmortal(type));
_Py_INCREF_IMMORTAL_STAT_INC();
return;
}
@ -357,7 +337,7 @@ static inline void
_Py_DECREF_TYPE(PyTypeObject *type)
{
if (!_PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
assert(_Py_IsImmortalLoose(type));
assert(_Py_IsImmortal(type));
_Py_DECREF_IMMORTAL_STAT_INC();
return;
}
@ -393,7 +373,7 @@ _PyObject_Init(PyObject *op, PyTypeObject *typeobj)
{
assert(op != NULL);
Py_SET_TYPE(op, typeobj);
assert(_PyType_HasFeature(typeobj, Py_TPFLAGS_HEAPTYPE) || _Py_IsImmortalLoose(typeobj));
assert(_PyType_HasFeature(typeobj, Py_TPFLAGS_HEAPTYPE) || _Py_IsImmortal(typeobj));
_Py_INCREF_TYPE(typeobj);
_Py_NewReference(op);
}

2
Include/object.h
View File

@ -81,7 +81,7 @@ whose size is determined when the object is allocated.
#else
#define PyObject_HEAD_INIT(type) \
{ \
{ _Py_IMMORTAL_REFCNT }, \
{ _Py_IMMORTAL_INITIAL_REFCNT }, \
(type) \
},
#endif

42
Include/refcount.h
View File

@ -21,25 +21,30 @@ cleanup during runtime finalization.
#if SIZEOF_VOID_P > 4
/*
In 64+ bit systems, an object will be marked as immortal by setting all of the
lower 32 bits of the reference count field, which is equal to: 0xFFFFFFFF
In 64+ bit systems, any object whose 32 bit reference count is >= 2**31
will be treated as immortal.
Using the lower 32 bits makes the value backwards compatible by allowing
C-Extensions without the updated checks in Py_INCREF and Py_DECREF to safely
increase and decrease the objects reference count. The object would lose its
immortality, but the execution would still be correct.
increase and decrease the objects reference count.
In order to offer sufficient resilience to C extensions using the stable ABI
compiled against 3.11 or earlier, we set the initial value near the
middle of the range (2**31, 2**32). That way the the refcount can be
off by ~1 billion without affecting immortality.
Reference count increases will use saturated arithmetic, taking advantage of
having all the lower 32 bits set, which will avoid the reference count to go
beyond the refcount limit. Immortality checks for reference count decreases will
be done by checking the bit sign flag in the lower 32 bits.
*/
#define _Py_IMMORTAL_REFCNT _Py_CAST(Py_ssize_t, UINT_MAX)
#define _Py_IMMORTAL_INITIAL_REFCNT ((Py_ssize_t)(3UL << 30))
#else
/*
In 32 bit systems, an object will be marked as immortal by setting all of the
lower 30 bits of the reference count field, which is equal to: 0x3FFFFFFF
In 32 bit systems, an object will be treated as immortal if its reference
count equals or exceeds _Py_IMMORTAL_MINIMUM_REFCNT (2**30).
Using the lower 30 bits makes the value backwards compatible by allowing
C-Extensions without the updated checks in Py_INCREF and Py_DECREF to safely
@ -47,9 +52,10 @@ increase and decrease the objects reference count. The object would lose its
immortality, but the execution would still be correct.
Reference count increases and decreases will first go through an immortality
check by comparing the reference count field to the immortality reference count.
check by comparing the reference count field to the minimum immortality refcount.
*/
#define _Py_IMMORTAL_REFCNT _Py_CAST(Py_ssize_t, UINT_MAX >> 2)
#define _Py_IMMORTAL_INITIAL_REFCNT ((Py_ssize_t)(3L << 29))
#define _Py_IMMORTAL_MINIMUM_REFCNT ((Py_ssize_t)(1L << 30))
#endif
// Py_GIL_DISABLED builds indicate immortal objects using `ob_ref_local`, which is
@ -90,7 +96,7 @@ PyAPI_FUNC(Py_ssize_t) Py_REFCNT(PyObject *ob);
#else
uint32_t local = _Py_atomic_load_uint32_relaxed(&ob->ob_ref_local);
if (local == _Py_IMMORTAL_REFCNT_LOCAL) {
return _Py_IMMORTAL_REFCNT;
return _Py_IMMORTAL_INITIAL_REFCNT;
}
Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&ob->ob_ref_shared);
return _Py_STATIC_CAST(Py_ssize_t, local) +
@ -109,9 +115,9 @@ static inline Py_ALWAYS_INLINE int _Py_IsImmortal(PyObject *op)
return (_Py_atomic_load_uint32_relaxed(&op->ob_ref_local) ==
_Py_IMMORTAL_REFCNT_LOCAL);
#elif SIZEOF_VOID_P > 4
return (_Py_CAST(PY_INT32_T, op->ob_refcnt) < 0);
return _Py_CAST(PY_INT32_T, op->ob_refcnt) < 0;
#else
return (op->ob_refcnt == _Py_IMMORTAL_REFCNT);
return op->ob_refcnt >= _Py_IMMORTAL_MINIMUM_REFCNT;
#endif
}
#define _Py_IsImmortal(op) _Py_IsImmortal(_PyObject_CAST(op))
@ -236,7 +242,7 @@ static inline Py_ALWAYS_INLINE void Py_INCREF(PyObject *op)
uint32_t new_local = local + 1;
if (new_local == 0) {
_Py_INCREF_IMMORTAL_STAT_INC();
// local is equal to _Py_IMMORTAL_REFCNT: do nothing
// local is equal to _Py_IMMORTAL_REFCNT_LOCAL: do nothing
return;
}
if (_Py_IsOwnedByCurrentThread(op)) {
@ -246,18 +252,14 @@ static inline Py_ALWAYS_INLINE void Py_INCREF(PyObject *op)
_Py_atomic_add_ssize(&op->ob_ref_shared, (1 << _Py_REF_SHARED_SHIFT));
}
#elif SIZEOF_VOID_P > 4
// Portable saturated add, branching on the carry flag and set low bits
PY_UINT32_T cur_refcnt = op->ob_refcnt_split[PY_BIG_ENDIAN];
PY_UINT32_T new_refcnt = cur_refcnt + 1;
if (new_refcnt == 0) {
if (((int32_t)cur_refcnt) < 0) {
// the object is immortal
_Py_INCREF_IMMORTAL_STAT_INC();
// cur_refcnt is equal to _Py_IMMORTAL_REFCNT: the object is immortal,
// do nothing
return;
}
op->ob_refcnt_split[PY_BIG_ENDIAN] = new_refcnt;
op->ob_refcnt_split[PY_BIG_ENDIAN] = cur_refcnt + 1;
#else
// Explicitly check immortality against the immortal value
if (_Py_IsImmortal(op)) {
_Py_INCREF_IMMORTAL_STAT_INC();
return;

4
Lib/test/test_builtin.py
View File

@ -2574,9 +2574,9 @@ class ShutdownTest(unittest.TestCase):
class ImmortalTests(unittest.TestCase):
if sys.maxsize < (1 << 32):
IMMORTAL_REFCOUNT = (1 << 30) - 1
IMMORTAL_REFCOUNT = 3 << 29
else:
IMMORTAL_REFCOUNT = (1 << 32) - 1
IMMORTAL_REFCOUNT = 3 << 30
IMMORTALS = (None, True, False, Ellipsis, NotImplemented, *range(-5, 257))

4
Misc/NEWS.d/next/Core_and_Builtins/2024-10-10-12-04-56.gh-issue-125174._8h6T7.rst Normal file
View File

@ -0,0 +1,4 @@
Make the handling of reference counts of immortal objects more robust.
Immortal objects with reference counts that deviate from their original
reference count by up to a billion (half a billion on 32 bit builds) are
still counted as immortal.

2
Modules/_asynciomodule.c
View File

@ -1387,7 +1387,7 @@ FutureObj_get_state(FutureObj *fut, void *Py_UNUSED(ignored))
default:
assert (0);
}
assert(_Py_IsImmortalLoose(ret));
assert(_Py_IsImmortal(ret));
return ret;
}

6
Objects/bytesobject.c
View File

@ -46,7 +46,7 @@ Py_LOCAL_INLINE(Py_ssize_t) _PyBytesWriter_GetSize(_PyBytesWriter *writer,
static inline PyObject* bytes_get_empty(void)
{
PyObject *empty = &EMPTY->ob_base.ob_base;
assert(_Py_IsImmortalLoose(empty));
assert(_Py_IsImmortal(empty));
return empty;
}
@ -119,7 +119,7 @@ PyBytes_FromStringAndSize(const char *str, Py_ssize_t size)
}
if (size == 1 && str != NULL) {
op = CHARACTER(*str & 255);
assert(_Py_IsImmortalLoose(op));
assert(_Py_IsImmortal(op));
return (PyObject *)op;
}
if (size == 0) {
@ -155,7 +155,7 @@ PyBytes_FromString(const char *str)
}
else if (size == 1) {
op = CHARACTER(*str & 255);
assert(_Py_IsImmortalLoose(op));
assert(_Py_IsImmortal(op));
return (PyObject *)op;
}

10
Objects/dictobject.c
View File

@ -416,6 +416,8 @@ _PyDict_DebugMallocStats(FILE *out)
#define DK_MASK(dk) (DK_SIZE(dk)-1)
#define _Py_DICT_IMMORTAL_INITIAL_REFCNT PY_SSIZE_T_MIN
static void free_keys_object(PyDictKeysObject *keys, bool use_qsbr);
/* PyDictKeysObject has refcounts like PyObject does, so we have the
@ -428,7 +430,8 @@ static void free_keys_object(PyDictKeysObject *keys, bool use_qsbr);
static inline void
dictkeys_incref(PyDictKeysObject *dk)
{
if (FT_ATOMIC_LOAD_SSIZE_RELAXED(dk->dk_refcnt) == _Py_IMMORTAL_REFCNT) {
if (FT_ATOMIC_LOAD_SSIZE_RELAXED(dk->dk_refcnt) < 0) {
assert(FT_ATOMIC_LOAD_SSIZE_RELAXED(dk->dk_refcnt) == _Py_DICT_IMMORTAL_INITIAL_REFCNT);
return;
}
#ifdef Py_REF_DEBUG
@ -440,7 +443,8 @@ dictkeys_incref(PyDictKeysObject *dk)
static inline void
dictkeys_decref(PyInterpreterState *interp, PyDictKeysObject *dk, bool use_qsbr)
{
if (FT_ATOMIC_LOAD_SSIZE_RELAXED(dk->dk_refcnt) == _Py_IMMORTAL_REFCNT) {
if (FT_ATOMIC_LOAD_SSIZE_RELAXED(dk->dk_refcnt) < 0) {
assert(FT_ATOMIC_LOAD_SSIZE_RELAXED(dk->dk_refcnt) == _Py_DICT_IMMORTAL_INITIAL_REFCNT);
return;
}
assert(FT_ATOMIC_LOAD_SSIZE(dk->dk_refcnt) > 0);
@ -586,7 +590,7 @@ estimate_log2_keysize(Py_ssize_t n)
* (which cannot fail and thus can do no allocation).
*/
static PyDictKeysObject empty_keys_struct = {
_Py_IMMORTAL_REFCNT, /* dk_refcnt */
_Py_DICT_IMMORTAL_INITIAL_REFCNT, /* dk_refcnt */
0, /* dk_log2_size */
0, /* dk_log2_index_bytes */
DICT_KEYS_UNICODE, /* dk_kind */

2
Objects/object.c
View File

@ -2453,7 +2453,7 @@ _Py_SetImmortalUntracked(PyObject *op)
op->ob_ref_local = _Py_IMMORTAL_REFCNT_LOCAL;
op->ob_ref_shared = 0;
#else
op->ob_refcnt = _Py_IMMORTAL_REFCNT;
op->ob_refcnt = _Py_IMMORTAL_INITIAL_REFCNT;
#endif
}

2
Objects/structseq.c
View File

@ -708,7 +708,7 @@ _PyStructSequence_FiniBuiltin(PyInterpreterState *interp, PyTypeObject *type)
assert(type->tp_name != NULL);
assert(type->tp_base == &PyTuple_Type);
assert((type->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN));
assert(_Py_IsImmortalLoose(type));
assert(_Py_IsImmortal(type));
// Cannot delete a type if it still has subclasses
if (_PyType_HasSubclasses(type)) {

8
Objects/typeobject.c
View File

@ -476,7 +476,7 @@ set_tp_bases(PyTypeObject *self, PyObject *bases, int initial)
assert(PyTuple_GET_SIZE(bases) == 1);
assert(PyTuple_GET_ITEM(bases, 0) == (PyObject *)self->tp_base);
assert(self->tp_base->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN);
assert(_Py_IsImmortalLoose(self->tp_base));
assert(_Py_IsImmortal(self->tp_base));
}
_Py_SetImmortal(bases);
}
@ -493,7 +493,7 @@ clear_tp_bases(PyTypeObject *self, int final)
Py_CLEAR(self->tp_bases);
}
else {
assert(_Py_IsImmortalLoose(self->tp_bases));
assert(_Py_IsImmortal(self->tp_bases));
_Py_ClearImmortal(self->tp_bases);
}
}
@ -558,7 +558,7 @@ clear_tp_mro(PyTypeObject *self, int final)
Py_CLEAR(self->tp_mro);
}
else {
assert(_Py_IsImmortalLoose(self->tp_mro));
assert(_Py_IsImmortal(self->tp_mro));
_Py_ClearImmortal(self->tp_mro);
}
}
@ -5966,7 +5966,7 @@ fini_static_type(PyInterpreterState *interp, PyTypeObject *type,
int isbuiltin, int final)
{
assert(type->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN);
assert(_Py_IsImmortalLoose((PyObject *)type));
assert(_Py_IsImmortal((PyObject *)type));
type_dealloc_common(type);

4
Python/bytecodes.c
View File

@ -381,7 +381,7 @@ dummy_func(
EXIT_IF(!PyLong_CheckExact(value_o));
STAT_INC(TO_BOOL, hit);
if (_PyLong_IsZero((PyLongObject *)value_o)) {
assert(_Py_IsImmortalLoose(value_o));
assert(_Py_IsImmortal(value_o));
DEAD(value);
res = PyStackRef_False;
}
@ -412,7 +412,7 @@ dummy_func(
EXIT_IF(!PyUnicode_CheckExact(value_o));
STAT_INC(TO_BOOL, hit);
if (value_o == &_Py_STR(empty)) {
assert(_Py_IsImmortalLoose(value_o));
assert(_Py_IsImmortal(value_o));
DEAD(value);
res = PyStackRef_False;
}

4
Python/executor_cases.c.h generated
View File

@ -402,7 +402,7 @@
}
STAT_INC(TO_BOOL, hit);
if (_PyLong_IsZero((PyLongObject *)value_o)) {
assert(_Py_IsImmortalLoose(value_o));
assert(_Py_IsImmortal(value_o));
res = PyStackRef_False;
}
else {
@ -455,7 +455,7 @@
}
STAT_INC(TO_BOOL, hit);
if (value_o == &_Py_STR(empty)) {
assert(_Py_IsImmortalLoose(value_o));
assert(_Py_IsImmortal(value_o));
res = PyStackRef_False;
}
else {

4
Python/generated_cases.c.h generated
View File

@ -7840,7 +7840,7 @@
DEOPT_IF(!PyLong_CheckExact(value_o), TO_BOOL);
STAT_INC(TO_BOOL, hit);
if (_PyLong_IsZero((PyLongObject *)value_o)) {
assert(_Py_IsImmortalLoose(value_o));
assert(_Py_IsImmortal(value_o));
res = PyStackRef_False;
}
else {
@ -7902,7 +7902,7 @@
DEOPT_IF(!PyUnicode_CheckExact(value_o), TO_BOOL);
STAT_INC(TO_BOOL, hit);
if (value_o == &_Py_STR(empty)) {
assert(_Py_IsImmortalLoose(value_o));
assert(_Py_IsImmortal(value_o));
res = PyStackRef_False;
}
else {

2
Python/import.c
View File

@ -1051,7 +1051,7 @@ del_cached_def(struct extensions_cache_value *value)
However, this decref would be problematic if the module def were
dynamically allocated, it were the last ref, and this function
were called with an interpreter other than the def's owner. */
assert(value->def == NULL || _Py_IsImmortalLoose(value->def));
assert(value->def == NULL || _Py_IsImmortal(value->def));
Py_XDECREF(value->def->m_base.m_copy);
value->def->m_base.m_copy = NULL;

1
Tools/cases_generator/analyzer.py
View File

@ -614,7 +614,6 @@ NON_ESCAPING_FUNCTIONS = (
"_Py_EnterRecursiveCallTstateUnchecked",
"_Py_ID",
"_Py_IsImmortal",
"_Py_IsImmortalLoose",
"_Py_LeaveRecursiveCallPy",
"_Py_LeaveRecursiveCallTstate",
"_Py_NewRef",