Hi Peter,
thanks for your reply.

quoted

      poll_wait(file, &tty->read_wait, wait);
      poll_wait(file, &tty->write_wait, wait);
-     if (input_available_p(tty, 1))
-             mask |= POLLIN | POLLRDNORM;
      if (tty->packet && tty->link->ctrl_status)
              mask |= POLLPRI | POLLIN | POLLRDNORM;
      if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
              mask |= POLLHUP;
      if (tty_hung_up_p(file))
              mask |= POLLHUP;
+     if (mask & POLLHUP)
+             tty_flush_to_ldisc(tty);

This isn't necessary for the tty_hung_up_p() case because, when the
poll() is woken from hangup, the read buffer has already been flushed (ie.,
cleared).

Plus, this waits even if input_available_p() would already return true.

Let me work on a patch for stable along the lines you suggest.

Francesco