2.4.0-test13-pre1 lockup: run_task_queue or tty_io are wrong

[Petr Vandrovec <vandrove@vc.cvut.cz>]

Hi,
  my 2.4.0-test13-pre1 just stopped answering to my keystrokes.
I've found that it is looping in tqueue_bh and flush_to_ldisc
still again and again.

  To my surprise I found that flush_to_ldisc() does

if (test_bit(TTY_DONT_FLIP, &tty_flags)) {
   queue_task(&tty->filp.tqueue, &tq_timer);
   return;
}

Looks ok. But only until you'll look at run_task_queue().
It now contains

  while (!list_empty(list)) {
      ...
  }

So postponing event to next timer tick does not work anymore.
It will stop cycling in run_task_queue and machine is dead
(unless you have some spare CPU).

Is current run_task_queue() behavior intentional, or is it
only bug introduced by changing task queue to list based
implementation?
					Thanks,
						Petr Vandrovec
						vandrove@vc.cvut.cz

P.S.: Yes, I know that I should bought faster computer so that
ldisc buffer does not overflow, but...
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