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gh-151673: Fix crash in warnings.warn() under memory pressure #151767

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gh-151673: Fix crash in warnings.warn() under memory pressure #151767

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20 changes: 19 additions & 1 deletion Lib/test/test_warnings/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,6 @@
import warnings as original_warnings
from warnings import deprecated


py_warnings = import_helper.import_fresh_module('_py_warnings')
py_warnings._set_module(py_warnings)

Expand Down Expand Up @@ -1237,6 +1236,25 @@ def test_issue31566(self):
support.swap_item(globals(), '__file__', None):
self.assertRaises(UserWarning, self.module.warn, 'bar')

@support.cpython_only
# Python built with Py_TRACE_REFS fail with a fatal error in
# _PyRefchain_Trace() on memory allocation error.
@unittest.skipIf(support.Py_TRACE_REFS, 'cannot test Py_TRACE_REFS build')
def test_issue151673(self):
# Skip this test if the _testcapi module isn't available.
_testcapi = import_helper.import_module('_testcapi')
# warn() shouldn't crash when the "<sys>" fallback filename
# can't be allocated under memory pressure.
code = """if 1:
import _testcapi, warnings
warnings.simplefilter("always")
_testcapi.set_nomemory(0)
warnings.warn("boom")
"""
rc, out, err = assert_python_failure("-c", code)
self.assertIn(rc, (1, 120))
self.assertIn(b'MemoryError', err)

@StanFromIreland StanFromIreland Jun 20, 2026

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Can we not make this a try/except?

@Ijtihed Ijtihed Jun 20, 2026

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skip is now handled inside the test trough import_helper.import_module



class WarningsDisplayTests(BaseTest):

Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-19-21-58-01.gh-issue-151673.Kx9mPq.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix a crash in :func:`warnings.warn` when the ``"<sys>"`` fallback filename
could not be allocated under memory pressure: :c:func:`!setup_context` left
the filename ``NULL`` and it was later passed to :c:func:`Py_DECREF`.
13 changes: 10 additions & 3 deletions Python/_warnings.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1031,9 +1031,18 @@ setup_context(Py_ssize_t stack_level,
}
}

/* Initialize the output references so handle_error can Py_XDECREF them
even when we bail out before they are assigned. */
*filename = NULL;
*registry = NULL;
*module = NULL;

if (f == NULL) {
globals = interp->sysdict;
*filename = PyUnicode_FromString("<sys>");
if (*filename == NULL) {
goto handle_error;
}
*lineno = 0;
}
else {
Expand All @@ -1043,8 +1052,6 @@ setup_context(Py_ssize_t stack_level,
Py_DECREF(f);
}

*module = NULL;

/* Setup registry. */
assert(globals != NULL);
assert(PyAnyDict_Check(globals));
Expand Down Expand Up @@ -1084,7 +1091,7 @@ setup_context(Py_ssize_t stack_level,
handle_error:
Py_XDECREF(*registry);
Py_XDECREF(*module);
Py_DECREF(*filename);
Py_XDECREF(*filename);
return 0;
}

Expand Down
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