Handle errors correctly in wait_helper in posixmodule.c

[sobolevn]

Bug report

There are several issues in this function:

1. Our traditional case, when all errors are overwritten in a sequence preparation:

   cpython/Modules/posixmodule.c

   Lines 9584 to 9609 in d2f1b0e

   	PyStructSequence_SET_ITEM(result, 0,
   	PyFloat_FromDouble(doubletime(ru->ru_utime)));
   	PyStructSequence_SET_ITEM(result, 1,
   	PyFloat_FromDouble(doubletime(ru->ru_stime)));
   	#define SET_INT(result, index, value)\
   	PyStructSequence_SET_ITEM(result, index, PyLong_FromLong(value))
   	SET_INT(result, 2, ru->ru_maxrss);
   	SET_INT(result, 3, ru->ru_ixrss);
   	SET_INT(result, 4, ru->ru_idrss);
   	SET_INT(result, 5, ru->ru_isrss);
   	SET_INT(result, 6, ru->ru_minflt);
   	SET_INT(result, 7, ru->ru_majflt);
   	SET_INT(result, 8, ru->ru_nswap);
   	SET_INT(result, 9, ru->ru_inblock);
   	SET_INT(result, 10, ru->ru_oublock);
   	SET_INT(result, 11, ru->ru_msgsnd);
   	SET_INT(result, 12, ru->ru_msgrcv);
   	SET_INT(result, 13, ru->ru_nsignals);
   	SET_INT(result, 14, ru->ru_nvcsw);
   	SET_INT(result, 15, ru->ru_nivcsw);
   	#undef SET_INT
   	if (PyErr_Occurred()) {
   	Py_DECREF(result);
   	return NULL;
   	}

2. PyLong_FromPid can return NULL, but this case is ignored

   cpython/Modules/posixmodule.c

   Line 9611 in d2f1b0e

   return Py_BuildValue("NiN", PyLong_FromPid(pid), status, result);

I have a PR ready.

Linked PRs

• gh-116404: Handle errors correctly in wait_helper in posixmodule #116405
• [3.12] gh-116404: Handle errors correctly in wait_helper in posixmodule (GH-116405) #116406
• [3.11] gh-116404: Handle errors correctly in wait_helper in posixmodule (GH-116405) #116407