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Title: gh-151763: Fix double decref in _PyPegen_raise_error_known_location() by manoj-marimuthu · Pull Request #151931 · python/cpython · GitHub

Open Graph Title: gh-151763: Fix double decref in _PyPegen_raise_error_known_location() by manoj-marimuthu · Pull Request #151931 · python/cpython

X Title: gh-151763: Fix double decref in _PyPegen_raise_error_known_location() by manoj-marimuthu · Pull Request #151931 · python/cpython

Description: The following PR addresses OOM-00019 from issue-151763. Issue: The _PyPegen_raise_error_known_location() in pegen_errors.c uses the Py_BuildValue function on a PyObject* called error_line with reference-stealing N format. tmp = Py_BuildValue("(OnnNnn)", p->tok->filename, lineno, col_number, error_line, end_lineno, end_col_number); when Py_BuildValue fails it returns NULL (ie tmp becomes NULL). when tmp == NULL, we do: if (!tmp) { goto error; } and goto error does: error: Py_XDECREF(errstr); Py_XDECREF(error_line); return NULL; This means that even if Py_BuildValue has decref'd error_line already, goto error repeats it which in turn trips _Py_NegativeRefcount: on debug builds. Reproduced using: import ast, _testcapi, faulthandler faulthandler.enable() src = "x y z\n" # generic invalid syntax -> located SyntaxError _testcapi.set_nomemory(55, 0) # fail every allocation from #55 onward try: ast.parse(src) # error_line built OK, then Py_BuildValue fails # -> N-arg already consumed -> error: decrefs it again finally: _testcapi.remove_mem_hooks() In debug build (tested on windows), it gives: _Py_NegativeRefcount: Assertion failed: object has negative ref count