From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759117AbXKLRCx (ORCPT ); Mon, 12 Nov 2007 12:02:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755640AbXKLRCn (ORCPT ); Mon, 12 Nov 2007 12:02:43 -0500 Received: from mho-02-bos.mailhop.org ([63.208.196.179]:64974 "EHLO mho-02-bos.mailhop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752858AbXKLRCm (ORCPT ); Mon, 12 Nov 2007 12:02:42 -0500 X-Greylist: delayed 421 seconds by postgrey-1.27 at vger.kernel.org; Mon, 12 Nov 2007 12:02:42 EST X-Mail-Handler: MailHop Outbound by DynDNS X-Originating-IP: 18.85.9.127 X-Report-Abuse-To: abuse@dyndns.com (see http://www.mailhop.org/outbound/abuse.html for abuse reporting information) X-MHO-User: U2FsdGVkX1+oc8wvR8ZB+62csnGd9U5X Message-ID: <4738872D.7020706@reed.com> Date: Mon, 12 Nov 2007 12:02:37 -0500 From: "David P. Reed" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.8.1.5) Gecko/20070727 Fedora/2.0.0.5-2.fc7 Thunderbird/2.0.0.5 Mnenhy/0.7.5.0 MIME-Version: 1.0 To: Thomas Gleixner , linux-kernel@vger.kernel.org CC: Allessandro Zummo Subject: [PATCH] time: fix typo that makes sync_cmos_clock erratic References: <466F0941.9060201@reed.com> <1181682498.8176.224.camel@chaos> <469578CD.3080609@reed.com> <1184216528.12353.203.camel@chaos> <1184218962.12353.209.camel@chaos> <46964352.7040301@reed.com> <1184253339.12353.223.camel@chaos> <469697C6.50903@reed.com> <1184274754.12353.254.camel@chaos> In-Reply-To: <1184274754.12353.254.camel@chaos> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: David P. Reed Fix a typo in ntp.c that has caused updating of the persistent (RTC) clock when synced to NTP to behave erratically. Signed-off-by: David P. Reed --- When debugging a freeze that arises on my AMD64 machines when I run the ntpd service, I added a number of printk's to monitor the sync_cmos_clock procedure. I discovered that it was not syncing to cmos RTC every 11 minutes as documented, but instead would keep trying every second for hours at a time. The reason turned out to be a typo in sync_cmos_clock, where it attempts to ensure that update_persistent_clock is called very close to 500 msec. after a 1 second boundary (required by the PC RTC's spec). That typo referred to "xtime" in one spot, rather than "now", which is derived from "xtime" but not equal to it. This makes the test erratic, creating a "coin-flip" that decides when update_persistent_clock is called - when it is called, which is rarely, it may be at any time during the one second period, rather than close to 500 msec, so the value written is needlessly incorrect, too. I rewrote the code to fix the typo and to be a little more clear about the logic that was intended here. I have thoroughly tested this on several x86_64 machines, and also on one 32-bit machine. I have also submitted a patch to fix the freeze cited above, but both patches are independent, and should be treated separately. The patch works in 2.6.24rc2, but it should also work in 2.6.23. Index: linux-2.6/kernel/time/ntp.c =================================================================== --- linux-2.6.orig/kernel/time/ntp.c +++ linux-2.6/kernel/time/ntp.c @@ -188,6 +188,7 @@ static DEFINE_TIMER(sync_cmos_timer, syn static void sync_cmos_clock(unsigned long dummy) { struct timespec now, next; + long delta_from_target_time; int fail = 1; /* @@ -205,7 +206,10 @@ static void sync_cmos_clock(unsigned lon return; getnstimeofday(&now); - if (abs(xtime.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2) + delta_from_target_time = abs(now.tv_nsec - (NSEC_PER_SEC / 2)); + + /* set CMOS clock, only if close enough to 500 msec point */ + if (delta_from_target_time <= tick_nsec / 2) fail = update_persistent_clock(now); next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec;