From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754308AbbFKWz4 (ORCPT ); Thu, 11 Jun 2015 18:55:56 -0400 Received: from mail-pd0-f176.google.com ([209.85.192.176]:36129 "EHLO mail-pd0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752962AbbFKWzK (ORCPT ); Thu, 11 Jun 2015 18:55:10 -0400 From: John Stultz To: linux-kernel@vger.kernel.org Cc: John Stultz , Prarit Bhargava , Daniel Bristot de Oliveira , Richard Cochran , Jan Kara , Jiri Bohac , Thomas Gleixner , Ingo Molnar Subject: [PATCH 4/5] ntp: Do leapsecond adjustment in adjtimex read path Date: Thu, 11 Jun 2015 15:54:56 -0700 Message-Id: <1434063297-28657-5-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1434063297-28657-1-git-send-email-john.stultz@linaro.org> References: <1434063297-28657-1-git-send-email-john.stultz@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since the leapsecond is applied at tick-time, this means there is a small window of time at the start of a leap-second where we cross into the next second before applying the leap. This patch modified adjtimex so that the leap-second is applied on the second edge. Providing more correct leapsecond behavior. This does make it so that adjtimex()'s returned time values can be inconsistent with time values read from gettimeofday() or clock_gettime(CLOCK_REALTIME,...) for a brief period of one tick at the leapsecond. However, those other interfaces do not provide the TIME_OOP time_state return that adjtimex() provides, which allows the leapsecond to be properly represented. They instead only see a time discontinuity, and cannot tell the first 23:59:59 from the repeated 23:59:59 leap second. This seems like a reasonable tradeoff given clock_gettime() / gettimeofday() cannot properly represent a leapsecond, and users likely care more about performance, while folks who are using adjtimex() more likely care about leap-second correctness. Cc: Prarit Bhargava Cc: Daniel Bristot de Oliveira Cc: Richard Cochran Cc: Jan Kara Cc: Jiri Bohac Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: John Stultz --- kernel/time/ntp.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 033743e..fb4d98c 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -740,6 +740,24 @@ int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai) if (!(time_status & STA_NANO)) txc->time.tv_usec /= NSEC_PER_USEC; + /* Handle leapsec adjustments */ + if (unlikely(ts->tv_sec >= ntp_next_leap_sec)) { + if ((time_state == TIME_INS) && (time_status & STA_INS)) { + result = TIME_OOP; + txc->tai++; + txc->time.tv_sec--; + } + if ((time_state == TIME_DEL) && (time_status & STA_DEL)) { + result = TIME_WAIT; + txc->tai--; + txc->time.tv_sec++; + } + if ((time_state == TIME_OOP) && + (ts->tv_sec == ntp_next_leap_sec)) { + result = TIME_WAIT; + } + } + return result; } -- 1.9.1