Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933254Ab0HEM2z (ORCPT ); Thu, 5 Aug 2010 08:28:55 -0400 Received: from mail.windriver.com ([147.11.1.11]:39881 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756027Ab0HEM2w (ORCPT ); Thu, 5 Aug 2010 08:28:52 -0400 From: Jason Wessel To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Jason Wessel , John Stultz , Thomas Gleixner , "H. Peter Anvin" Subject: [PATCH] timekeeping: Fix overflow in rawtime tv_nsec on 32 bit archs Date: Thu, 5 Aug 2010 07:28:32 -0500 Message-Id: <1281011312-23499-1-git-send-email-jason.wessel@windriver.com> X-Mailer: git-send-email 1.6.4.rc1 X-OriginalArrivalTime: 05 Aug 2010 12:28:38.0534 (UTC) FILETIME=[BB305A60:01CB3499] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2433 Lines: 63 The tv_nsec is a long and when added to the shift value it can wrap and become negative which later causes looping problems in the getrawmonotonic(). The edge case occurs when the system has slept for a short period of time of ~2 seconds. A trace printk of the values in this patch illustrate the problem: ftrace time stamp: log 43.716079: logarithmic_accumulation: raw_shift: 3d0913 tv_nsec d687faa 43.718513: logarithmic_accumulation: raw_shift: 3d0913 tv_nsec da588bd 43.722161: logarithmic_accumulation: raw_shift: 3d0913 tv_nsec de291d0 46.349925: logarithmic_accumulation: raw_shift: 7a122600 tv_nsec e1f9ae3 46.349930: logarithmic_accumulation: raw_shift: 1e848980 tv_nsec 8831c0e3 The kernel starts looping at 46.349925 in the getrawmonotonic() due to the negative value from adding the raw_shift to tv_nsec. A simple solution is to process the raw_shift separately from the tv_nsec using the same type of loop in logarithmic_accumulation(). Signed-off-by: Jason Wessel CC: John Stultz CC: Thomas Gleixner CC: H. Peter Anvin --- kernel/time/timekeeping.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index caf8d4d..1762282 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -736,6 +736,7 @@ static void timekeeping_adjust(s64 offset) static cycle_t logarithmic_accumulation(cycle_t offset, int shift) { u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift; + u64 raw_shift; /* If the offset is smaller then a shifted interval, do nothing */ if (offset < timekeeper.cycle_interval<= NSEC_PER_SEC) { + raw_shift -= NSEC_PER_SEC; + raw_time.tv_sec++; + } + raw_time.tv_nsec += raw_shift; while (raw_time.tv_nsec >= NSEC_PER_SEC) { raw_time.tv_nsec -= NSEC_PER_SEC; raw_time.tv_sec++; -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/