From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754732AbbIMLHi (ORCPT ); Sun, 13 Sep 2015 07:07:38 -0400 Received: from terminus.zytor.com ([198.137.202.10]:43678 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752294AbbIMLHe (ORCPT ); Sun, 13 Sep 2015 07:07:34 -0400 Date: Sun, 13 Sep 2015 04:07:02 -0700 From: tip-bot for John Stultz Message-ID: Cc: prarit@redhat.com, torvalds@linux-foundation.org, nunojpg@gmail.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, richardcochran@gmail.com, mlichvar@redhat.com, peterz@infradead.org, mingo@kernel.org, john.stultz@linaro.org, hpa@zytor.com Reply-To: mingo@kernel.org, hpa@zytor.com, john.stultz@linaro.org, mlichvar@redhat.com, richardcochran@gmail.com, peterz@infradead.org, tglx@linutronix.de, nunojpg@gmail.com, linux-kernel@vger.kernel.org, prarit@redhat.com, torvalds@linux-foundation.org In-Reply-To: <1441840051-20244-1-git-send-email-john.stultz@linaro.org> References: <1441840051-20244-1-git-send-email-john.stultz@linaro.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:timers/urgent] time: Fix timekeeping_freqadjust()' s incorrect use of abs() instead of abs64() Git-Commit-ID: 2619d7e9c92d524cb155ec89fd72875321512e5b X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 2619d7e9c92d524cb155ec89fd72875321512e5b Gitweb: http://git.kernel.org/tip/2619d7e9c92d524cb155ec89fd72875321512e5b Author: John Stultz AuthorDate: Wed, 9 Sep 2015 16:07:30 -0700 Committer: Ingo Molnar CommitDate: Sun, 13 Sep 2015 10:30:47 +0200 time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64() The internal clocksteering done for fine-grained error correction uses a logarithmic approximation, so any time adjtimex() adjusts the clock steering, timekeeping_freqadjust() quickly approximates the correct clock frequency over a series of ticks. Unfortunately, the logic in timekeeping_freqadjust(), introduced in commit: dc491596f639 ("timekeeping: Rework frequency adjustments to work better w/ nohz") used the abs() function with a s64 error value to calculate the size of the approximated adjustment to be made. Per include/linux/kernel.h: "abs() should not be used for 64-bit types (s64, u64, long long) - use abs64()". Thus on 32-bit platforms, this resulted in the clocksteering to take a quite dampended random walk trying to converge on the proper frequency, which caused the adjustments to be made much slower then intended (most easily observed when large adjustments are made). This patch fixes the issue by using abs64() instead. Reported-by: Nuno Gonçalves Tested-by: Nuno Goncalves Signed-off-by: John Stultz Cc: # v3.17+ Cc: Linus Torvalds Cc: Miroslav Lichvar Cc: Peter Zijlstra Cc: Prarit Bhargava Cc: Richard Cochran Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1441840051-20244-1-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar --- kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index f6ee2e6..3739ac6 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1614,7 +1614,7 @@ static __always_inline void timekeeping_freqadjust(struct timekeeper *tk, negative = (tick_error < 0); /* Sort out the magnitude of the correction */ - tick_error = abs(tick_error); + tick_error = abs64(tick_error); for (adj = 0; tick_error > interval; adj++) tick_error >>= 1;