Re: testing/pre-7 and do_poll()

[Adam Heath <doogie@debian.org>]

On Sun, 10 Jan 1999, Chip Salzenberg wrote:

> According to Linus Torvalds:
> > There's a "pre-7.gz" on ftp.kernel.org in testing, anybody interested?
> 
> Got it, like it -- *except* the fix for overflow in do_poll() is a
> little bit off.  Quoting testing/pre-7:
> 
> 	if (timeout) {
> 		/* Carefula about overflow in the intermediate values */
> 		if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ)
> 			timeout = (timeout*HZ+999)/1000+1;
> 		else /* Negative or overflow */
> 			timeout = MAX_SCHEDULE_TIMEOUT;
> 	}
> 
> 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.

A/(B/C) = A * (C / B) = A / B * C (done this way to eliminate overflow)

MAX_SCHEDULE_TIMEOUT / 1000 * HZ

Adam


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