Правильно я понимаю, что маска обработчика блокирует соответствующие в ней сигналы?
sa_mask specifies a mask of signals which should be blocked (i.e.,
added to the signal mask of the thread in which the signal handler is
invoked) during execution of the signal handler. In addition, the
signal which triggered the handler will be blocked, unless the
SA_NODEFER flag is used.