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GeezerVison is showing github.com — [3.13] gh-122527: Fix a crash on deallocation of `PyStructSequence` (GH-122577) by miss-islington · Pull Request #122625 · python/cpython

[3.13] gh-122527: Fix a crash on deallocation of PyStructSequence (GH-122577) #122625

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Merged
Yhg1s merged 1 commit into python:3.13 from miss-islington:backport-4b63cd1-3.13
Sep 2, 2024

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Merged

[3.13] gh-122527: Fix a crash on deallocation of PyStructSequence (GH-122577) #122625

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gh-122527: Fix a crash on deallocation of `PyStructSequence` (GH-122577)
colesbury Aug 2, 2024
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13 changes: 13 additions & 0 deletions 13 Lib/test/test_structseq.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,10 @@
import os
import pickle
import re
import textwrap
import time
import unittest
from test.support import script_helper


class StructSeqTest(unittest.TestCase):
Expand Down Expand Up @@ -342,6 +344,17 @@ def test_copy_replace_with_unnamed_fields(self):
with self.assertRaisesRegex(TypeError, error_message):
copy.replace(r, st_mode=1, error=2)

def test_reference_cycle(self):
# gh-122527: Check that a structseq that's part of a reference cycle
# with its own type doesn't crash. Previously, if the type's dictionary
# was cleared first, the structseq instance would crash in the
# destructor.
script_helper.assert_python_ok("-c", textwrap.dedent(r"""
import time
t = time.gmtime()
type(t).refcyle = t
"""))


if __name__ == "__main__":
unittest.main()
3 changes: 2 additions & 1 deletion 3 Lib/test/test_sys.py
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Expand Up @@ -1822,7 +1822,8 @@ def test_pythontypes(self):
# symtable entry
# XXX
# sys.flags
check(sys.flags, vsize('') + self.P * len(sys.flags))
# FIXME: The +1 will not be necessary once gh-122575 is fixed
check(sys.flags, vsize('') + self.P * (1 + len(sys.flags)))

def test_asyncgen_hooks(self):
old = sys.get_asyncgen_hooks()
Expand Down
4 changes: 4 additions & 0 deletions 4 Misc/NEWS.d/next/Core_and_Builtins/2024-08-01-19-13-58.gh-issue-122527.eztso6.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Fix a crash that occurred when a ``PyStructSequence`` was deallocated after
its type's dictionary was cleared by the GC. The type's
:c:member:`~PyTypeObject.tp_basicsize` now accounts for non-sequence fields
that aren't included in the :c:macro:`Py_SIZE` of the sequence.
28 changes: 22 additions & 6 deletions 28 Objects/structseq.c
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Original file line number Diff line number Diff line change
Expand Up @@ -41,12 +41,20 @@ get_type_attr_as_size(PyTypeObject *tp, PyObject *name)
get_type_attr_as_size(tp, &_Py_ID(n_sequence_fields))
#define REAL_SIZE_TP(tp) \
get_type_attr_as_size(tp, &_Py_ID(n_fields))
#define REAL_SIZE(op) REAL_SIZE_TP(Py_TYPE(op))
#define REAL_SIZE(op) get_real_size((PyObject *)op)

#define UNNAMED_FIELDS_TP(tp) \
get_type_attr_as_size(tp, &_Py_ID(n_unnamed_fields))
#define UNNAMED_FIELDS(op) UNNAMED_FIELDS_TP(Py_TYPE(op))

static Py_ssize_t
get_real_size(PyObject *op)
{
// Compute the real size from the visible size (i.e., Py_SIZE()) and the
// number of non-sequence fields accounted for in tp_basicsize.
Py_ssize_t hidden = Py_TYPE(op)->tp_basicsize - offsetof(PyStructSequence, ob_item);
return Py_SIZE(op) + hidden / sizeof(PyObject *);
}

PyObject *
PyStructSequence_New(PyTypeObject *type)
Expand Down Expand Up @@ -120,6 +128,9 @@ structseq_dealloc(PyStructSequence *obj)
PyObject_GC_UnTrack(obj);

PyTypeObject *tp = Py_TYPE(obj);
// gh-122527: We can't use REAL_SIZE_TP() or any macros that access the
// type's dictionary here, because the dictionary may have already been
// cleared by the garbage collector.
size = REAL_SIZE(obj);
for (i = 0; i < size; ++i) {
Py_XDECREF(obj->ob_item[i]);
Expand Down Expand Up @@ -565,10 +576,14 @@ initialize_members(PyStructSequence_Desc *desc,

static void
initialize_static_fields(PyTypeObject *type, PyStructSequence_Desc *desc,
PyMemberDef *tp_members, unsigned long tp_flags)
PyMemberDef *tp_members, Py_ssize_t n_members,
unsigned long tp_flags)
{
type->tp_name = desc->name;
type->tp_basicsize = sizeof(PyStructSequence) - sizeof(PyObject *);
// Account for hidden members in tp_basicsize because they are not
// included in the variable size.
Py_ssize_t n_hidden = n_members - desc->n_in_sequence;
type->tp_basicsize = sizeof(PyStructSequence) + (n_hidden - 1) * sizeof(PyObject *);
type->tp_itemsize = sizeof(PyObject *);
type->tp_dealloc = (destructor)structseq_dealloc;
type->tp_repr = (reprfunc)structseq_repr;
Expand Down Expand Up @@ -621,7 +636,7 @@ _PyStructSequence_InitBuiltinWithFlags(PyInterpreterState *interp,
if (members == NULL) {
goto error;
}
initialize_static_fields(type, desc, members, tp_flags);
initialize_static_fields(type, desc, members, n_members, tp_flags);

_Py_SetImmortal((PyObject *)type);
}
Expand Down Expand Up @@ -684,7 +699,7 @@ PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)
if (members == NULL) {
return -1;
}
initialize_static_fields(type, desc, members, 0);
initialize_static_fields(type, desc, members, n_members, 0);
if (initialize_static_type(type, desc, n_members, n_unnamed_members) < 0) {
PyMem_Free(members);
return -1;
Expand Down Expand Up @@ -760,7 +775,8 @@ _PyStructSequence_NewType(PyStructSequence_Desc *desc, unsigned long tp_flags)
/* The name in this PyType_Spec is statically allocated so it is */
/* expected that it'll outlive the PyType_Spec */
spec.name = desc->name;
spec.basicsize = sizeof(PyStructSequence) - sizeof(PyObject *);
Py_ssize_t hidden = n_members - desc->n_in_sequence;
spec.basicsize = (int)(sizeof(PyStructSequence) + (hidden - 1) * sizeof(PyObject *));
spec.itemsize = sizeof(PyObject *);
spec.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | tp_flags;
spec.slots = slots;
Expand Down
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