Re: testing/pre-7 and do_poll()

Chip Salzenberg (chip@perlsupport.com)
Mon, 11 Jan 1999 01:26:21 -0500

According to Linus Torvalds:
> On Sun, 10 Jan 1999, Chip Salzenberg wrote:
> > However, the maximum legal millisecond timeout isn't (as shown)
> > MAX_SCHEDULE_TIMEOUT/HZ, but rather MAX_SCHEDULE_TIMEOUT/(1000/HZ).
> > So this code will turn some large timeouts into MAX_SCHEDULE_TIMEOUT
> > unnecessarily.
>
> Note the comment (and do NOT look at the speeling). In particular,
> we need to make sure the _intermediate_ value doesn' toverflow.

Of course; that's obvious. What's perhaps less obvious is that I'm
suggesting a change in the calculation of timeout -- a change which
avoids the creation of unnecessarily large _intermediate_ values.

> > ! if (timeout < 0)
> > ! timeout = MAX_SCHEDULE_TIMEOUT;
> > ! else if (timeout)
> > ! timeout = ROUND_UP(timeout, 1000/HZ);
>
> Eh? And re-introduce the original bug?

Well, I forgot the (unsigned long) cast, as someone else noted:

timeout = ROUND_UP((unsigned long) timeout, 1000/HZ);

Otherwise, the code is Just Right.

-- 
Chip Salzenberg      - a.k.a. -      <chip@perlsupport.com>
      "When do you work?"   "Whenever I'm not busy."


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/