From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from neon.transmeta.com (neon-best.transmeta.com [206.184.214.10]) by kvack.org (8.8.7/8.8.7) with ESMTP id BAA27503 for ; Mon, 11 Jan 1999 01:03:40 -0500 Date: Sun, 10 Jan 1999 22:02:47 -0800 (PST) From: Linus Torvalds Subject: Re: testing/pre-7 and do_poll() In-Reply-To: <19990110183356.C262@perlsupport.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Chip Salzenberg Cc: linux-kernel@vger.rutgers.edu, linux-mm@kvack.org List-ID: On Sun, 10 Jan 1999, Chip Salzenberg wrote: > > 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. Note the comment (and do NOT look at the speeling). In particular, we need to make sure the _intermediate_ value doesn' toverflow. We could do that by using 64-bit arithmetic, but let's not. > ! if (timeout < 0) > ! timeout = MAX_SCHEDULE_TIMEOUT; > ! else if (timeout) > ! timeout = ROUND_UP(timeout, 1000/HZ); Eh? And re-introduce the original bug? Linus -- This is a majordomo managed list. To unsubscribe, send a message with the body 'unsubscribe linux-mm me@address' to: majordomo@kvack.org