From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752552AbbJFIGO (ORCPT ); Tue, 6 Oct 2015 04:06:14 -0400 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:53261 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752004AbbJFIGC (ORCPT ); Tue, 6 Oct 2015 04:06:02 -0400 X-Sasl-enc: f8gCtfhGRYe//Dswp5wGfiNv06d78cjxgrH6hwe6DRZm 1444118758 Date: Tue, 6 Oct 2015 09:05:51 +0100 From: Greg KH To: Nuno =?iso-8859-1?Q?Gon=E7alves?= Cc: stable@vger.kernel.org, linux-tip-commits@vger.kernel.org, mingo@kernel.org, hpa@zytor.com, john.stultz@linaro.org, mlichvar@redhat.com, richardcochran@gmail.com, peterz@infradead.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, prarit@redhat.com, torvalds@linux-foundation.org Subject: Re: [tip:timers/urgent] time: Fix timekeeping_freqadjust()' s incorrect use of abs() instead of abs64() Message-ID: <20151006080551.GE18449@kroah.com> References: <1441840051-20244-1-git-send-email-john.stultz@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 05, 2015 at 04:10:28PM +0100, Nuno Gonçalves wrote: > On Sun, Sep 13, 2015 at 12:07 PM, tip-bot for John Stultz > wrote: > > 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; > > > > I think this got lost on its way to the linux-stable queue (or I don't > understand the stable rules). It's still in the "todo" queue, along with 159 other patches that I have yet to get to :( thanks, greg k-h