gh-147998: Fix possible memory leak in _pop_preserved (crossinterp.c)

[maurycy]

cpython/Python/crossinterp.c

Line 2968 in 7817651

_PyXI_namespace *xidata = _create_sharedns(session->_preserved);

cpython/Python/crossinterp.c

Line 2991 in 7817651

if (xidata != NULL) {

The xidata seems to be shadowed inside the else, and the error: path does not see it, resulting in a (small) memory leak.

It's no longer reproducible:

2026-04-02T13:17:22.653113102+0000 maurycy@weiss /home/maurycy/cpython (maurycy/pop_preserved_shadowing) % ASAN_OPTIONS=detect_leaks=1 ./python.exe -c "
import _interpreters as _interp

interp_id = _interp.create()

# The callable must SUCCEED but return something non-shareable.
# globals() returns a dict with module refs -- not shareable.
for i in range(200):
    try:
        _interp.call(interp_id, globals)
    except Exception:
        pass

_interp.destroy(interp_id)
print('done')
"
done
2026-04-02T13:17:52.741094846+0000 maurycy@weiss /home/maurycy/cpython (maurycy/pop_preserved_shadowing) % 

• Issue: Avoid memory leak in _pop_preserved() #147998

[serhiy-storchaka]

LGTM. 👍

[serhiy-storchaka]

Could you please add a NEWS entry?

_pop_preserved() is only used in _PyXI_Exit(), which is used in functions exec(), run_string(), run_func(), call(), and set___main___attrs() of the private module _interpreters (and finally used in some public API). The description should use some general roundabout words to avoid touching internal details.

[maurycy]

@serhiy-storchaka 6b415f5