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[3.14] gh-159739: Protect list storage while reporting its size (GH-160196) #160364

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Merged
JelleZijlstra merged 1 commit into from
Oct 22, 2026
Merged

[3.14] gh-159739: Protect list storage while reporting its size (GH-160196) #160364

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-10-21-21-26-10.gh-issue-159739.Aw61LR.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix a race in ``list.__sizeof__()`` when a list is concurrently resized on a free-threaded build.
4 changes: 3 additions & 1 deletion Objects/listobject.c
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Expand Up @@ -137,7 +137,7 @@
py_list_resize(PyListObject *self, Py_ssize_t newsize)
{
size_t new_allocated, target_bytes;
Py_ssize_t allocated = self->allocated;

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GitHub Actions / Cross build Linux 

unused variable ‘allocated’ [-Wunused-variable]

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GitHub Actions / Address sanitizer (ubuntu-26.04) 

unused variable ‘allocated’ [-Wunused-variable]

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GitHub Actions / Ubuntu (installed) / build, install and test 

unused variable ‘allocated’ [-Wunused-variable]

/* This over-allocates proportional to the list size, making room
* for additional growth. The over-allocation is mild, but is
Expand Down Expand Up @@ -3560,10 +3560,12 @@
{
size_t res = _PyObject_SIZE(Py_TYPE(self));
#ifdef Py_GIL_DISABLED
PyObject **ob_item = _Py_atomic_load_ptr(&self->ob_item);
Py_BEGIN_CRITICAL_SECTION(self);
PyObject **ob_item = self->ob_item;
if (ob_item != NULL) {
res += list_capacity(ob_item) * sizeof(PyObject *);
}
Py_END_CRITICAL_SECTION();
#else
res += (size_t)self->allocated * sizeof(PyObject *);
#endif
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