testing/pre-7 and do_poll()

Chip Salzenberg (chip@perlsupport.com)
Sun, 10 Jan 1999 18:33:56 -0500

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.

Therefore, I suggest this patch:

Index: fs/select.c
*************** asmlinkage int sys_poll(struct pollfd *
*** 336,346 ****
goto out;

! 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;
! }

err = -ENOMEM;
--- 336,343 ----
goto out;

! if (timeout < 0)
! timeout = MAX_SCHEDULE_TIMEOUT;
! else if (timeout)
! timeout = ROUND_UP(timeout, 1000/HZ);

err = -ENOMEM;

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


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