Hi Eli,

The problem is normal_poll in drivers/char/n_tty.c:

 > if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS)
 >                mask |= POLLOUT | POLLWRNORM;

It assumes that a following write will succeed if less than 256 bytes 
are in the write buffer right now. This assumption is wrong for 
con_write_room: if the console is stopped, it returns 0 bytes buffer 
size (con_write_room()). Dito for pty_write_room.

The attached patch fixes your test case, but I don't understand tty 
devices good enough to guarantee anything.

--
    Manfred