Re: [BUG] mysterious tty deadlock

[Andrew Morton <akpm@zip.com.au>]

Russell King wrote:
> 
> ...
> > --- 2.5.32/drivers/serial/core.c~serial-race  Wed Aug 28 15:22:22 2002
> > +++ 2.5.32-akpm/drivers/serial/core.c Wed Aug 28 15:22:26 2002
> > @@ -1315,13 +1315,14 @@ static void uart_wait_until_sent(struct
> >        * 'timeout' / 'expire' give us the maximum amount of time
> >        * we wait.
> >        */
> > +     set_current_state(TASK_INTERRUPTIBLE);
> >       while (!port->ops->tx_empty(port)) {
> > -             set_current_state(TASK_INTERRUPTIBLE);
> >               schedule_timeout(char_time);
> >               if (signal_pending(current))
> >                       break;
> >               if (time_after(jiffies, expire))
> >                       break;
> > +             set_current_state(TASK_INTERRUPTIBLE);
> >       }
> >       set_current_state(TASK_RUNNING); /* might not be needed */
> >  }
> 
> Patch looks good, as far as correctness goes.  However, since char_time
> will be the amount of time for one character, we should never sleep long
> enough for the user to notice this slip-up.
> 
> If people are seeing deadlocks, I agree with wli that there's something
> very wrong elsewhere.

Well Bill's trace is claiming that we're doing a schedule_timeout(0x7fffffff)
for some reason.

But yes, he seems to be able to hit it too frequently for this to be
the cause.