Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756907Ab0HIVUm (ORCPT ); Mon, 9 Aug 2010 17:20:42 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:44500 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756589Ab0HIVUj (ORCPT ); Mon, 9 Aug 2010 17:20:39 -0400 From: John Stultz To: linux-kernel@vger.kernel.org Cc: Jason Wessel , John Stultz , Thomas Gleixner , "H. Peter Anvin" Subject: [PATCH 1/2] timekeeping: Fix overflow in rawtime tv_nsec on 32 bit archs Date: Mon, 9 Aug 2010 14:20:09 -0700 Message-Id: <1281388810-25806-2-git-send-email-johnstul@us.ibm.com> X-Mailer: git-send-email 1.6.0.4 In-Reply-To: <1281388810-25806-1-git-send-email-johnstul@us.ibm.com> References: <1281388810-25806-1-git-send-email-johnstul@us.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2650 Lines: 73 From: Jason Wessel The tv_nsec is a long and when added to the shifted interval 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: 3d0913 tv_nsec d687faa 43.718513: logarithmic_accumulation: raw: 3d0913 tv_nsec da588bd 43.722161: logarithmic_accumulation: raw: 3d0913 tv_nsec de291d0 46.349925: logarithmic_accumulation: raw: 7a122600 tv_nsec e1f9ae3 46.349930: logarithmic_accumulation: raw: 1e848980 tv_nsec 8831c0e3 The kernel starts looping at 46.349925 in the getrawmonotonic() due to the negative value from adding the raw value to tv_nsec. A simple solution is to accumulate into a u64, and then normalize it to a timespec_t. Signed-off-by: Jason Wessel Reworked variable names and sipmlified some of the code. Signed-off-by: John Stultz CC: Thomas Gleixner CC: H. Peter Anvin --- kernel/time/timekeeping.c | 11 +++++++---- 1 files changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index e14c839..e960d82 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -690,6 +690,7 @@ 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_nsecs; /* If the offset is smaller then a shifted interval, do nothing */ if (offset < timekeeper.cycle_interval<= NSEC_PER_SEC) { - raw_time.tv_nsec -= NSEC_PER_SEC; + /* Accumulate raw time */ + raw_nsecs = timekeeper.raw_interval << shift; + raw_nsecs += raw_time.tv_nsec; + while (raw_nsecs >= NSEC_PER_SEC) { + raw_nsecs -= NSEC_PER_SEC; raw_time.tv_sec++; } + raw_time.tv_nsec = raw_nsecs; /* Accumulate error between NTP and clock interval */ timekeeper.ntp_error += tick_length << shift; -- 1.6.0.4 -- 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/