From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752002AbbCSCov (ORCPT ); Wed, 18 Mar 2015 22:44:51 -0400 Received: from m50-111.126.com ([123.125.50.111]:50415 "EHLO m50-111.126.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756AbbCSCos (ORCPT ); Wed, 18 Mar 2015 22:44:48 -0400 From: Xunlei Pang To: linux-kernel@vger.kernel.org Cc: rtc-linux@googlegroups.com, Thomas Gleixner , Alessandro Zummo , John Stultz , Arnd Bergmann , Peter Zijlstra , Xunlei Pang Subject: [PATCH 1/2] time: Fix a bug in timekeeping_suspend() with no persistent clock Date: Thu, 19 Mar 2015 10:42:31 +0800 Message-Id: <1426732952-26893-1-git-send-email-xlpang@126.com> X-Mailer: git-send-email 1.9.1 X-CM-TRANSID: jtKowAAndI2hNwpVuhRjAA--.398S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxXr43Cry7Kw43Aw4DXrW7twb_yoW5CFyfpr W7Cr13Ka1DXFy3CrnFyFnru3s0gws5tw4UZr9Ik34xC347Xrs3Gr4Fk3WrtryqvryfAr98 ZF1Iq3y5u3y8GF7anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jqZXOUUUUU= X-Originating-IP: [210.21.223.3] X-CM-SenderInfo: p0ost0bj6rjloofrz/1tbiWwjBv1PM7hbVjgAAsR Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xunlei Pang When there's no persistent clock, normally timekeeping_suspend_time should always be zero, but this can break in timekeeping_suspend(). At T1, there was a system suspend, so old_delta was assigned T1. After some time, one time adjustment happened, and xtime got the value of T1-dt(0s --- kernel/time/timekeeping.c | 36 +++++++++++++++++++----------------- 1 file changed, 19 insertions(+), 17 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 1345e63..605da5c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1127,7 +1127,7 @@ void __init timekeeping_init(void) raw_spin_unlock_irqrestore(&timekeeper_lock, flags); } -/* time in seconds when suspend began */ +/* time in seconds when suspend began for persistent clock */ static struct timespec64 timekeeping_suspend_time; /** @@ -1304,24 +1304,26 @@ int timekeeping_suspend(void) timekeeping_forward_now(tk); timekeeping_suspended = 1; - /* - * To avoid drift caused by repeated suspend/resumes, - * which each can add ~1 second drift error, - * try to compensate so the difference in system time - * and persistent_clock time stays close to constant. - */ - delta = timespec64_sub(tk_xtime(tk), timekeeping_suspend_time); - delta_delta = timespec64_sub(delta, old_delta); - if (abs(delta_delta.tv_sec) >= 2) { + if (has_persistent_clock()) { /* - * if delta_delta is too large, assume time correction - * has occured and set old_delta to the current delta. + * To avoid drift caused by repeated suspend/resumes, + * which each can add ~1 second drift error, + * try to compensate so the difference in system time + * and persistent_clock time stays close to constant. */ - old_delta = delta; - } else { - /* Otherwise try to adjust old_system to compensate */ - timekeeping_suspend_time = - timespec64_add(timekeeping_suspend_time, delta_delta); + delta = timespec64_sub(tk_xtime(tk), timekeeping_suspend_time); + delta_delta = timespec64_sub(delta, old_delta); + if (abs(delta_delta.tv_sec) >= 2) { + /* + * if delta_delta is too large, assume time correction + * has occurred and set old_delta to the current delta. + */ + old_delta = delta; + } else { + /* Otherwise try to adjust old_system to compensate */ + timekeeping_suspend_time = + timespec64_add(timekeeping_suspend_time, delta_delta); + } } timekeeping_update(tk, TK_MIRROR); -- 1.9.1