From: Greg KH <greg@kroah.com>
To: "Nuno Gonçalves" <nunojpg@gmail.com>
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()
Date: Tue, 6 Oct 2015 09:05:51 +0100 [thread overview]
Message-ID: <20151006080551.GE18449@kroah.com> (raw)
In-Reply-To: <CAEXMXLSaLfbZSGVQVX10wp2vLNZfamRsy+uLNuc7Jpw5nmpZPg@mail.gmail.com>
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
> <tipbot@zytor.com> wrote:
> > Commit-ID: 2619d7e9c92d524cb155ec89fd72875321512e5b
> > Gitweb: http://git.kernel.org/tip/2619d7e9c92d524cb155ec89fd72875321512e5b
> > Author: John Stultz <john.stultz@linaro.org>
> > AuthorDate: Wed, 9 Sep 2015 16:07:30 -0700
> > Committer: Ingo Molnar <mingo@kernel.org>
> > 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 <nunojpg@gmail.com>
> > Tested-by: Nuno Goncalves <nunojpg@gmail.com>
> > Signed-off-by: John Stultz <john.stultz@linaro.org>
> > Cc: <stable@vger.kernel.org> # v3.17+
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Miroslav Lichvar <mlichvar@redhat.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Prarit Bhargava <prarit@redhat.com>
> > Cc: Richard Cochran <richardcochran@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Link: http://lkml.kernel.org/r/1441840051-20244-1-git-send-email-john.stultz@linaro.org
> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > ---
> > 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
prev parent reply other threads:[~2015-10-06 8:06 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-09 23:07 [PATCH 1/2] time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64() John Stultz
2015-09-09 23:07 ` [PATCH 2/2 (v2)] kselftest: timers: Add adjtick test to validate adjtimex() tick adjustments John Stultz
2015-09-10 12:02 ` Miroslav Lichvar
2015-09-10 17:42 ` John Stultz
2015-09-10 18:14 ` John Stultz
2015-09-14 14:48 ` Miroslav Lichvar
2015-10-02 20:25 ` John Stultz
2015-10-02 20:27 ` John Stultz
2015-10-02 20:49 ` John Stultz
2015-09-13 8:32 ` [PATCH 1/2] time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64() Ingo Molnar
2015-09-14 23:24 ` John Stultz
2015-09-13 11:07 ` [tip:timers/urgent] time: Fix timekeeping_freqadjust()' s " tip-bot for John Stultz
2015-10-05 15:10 ` Nuno Gonçalves
2015-10-06 8:05 ` Greg KH [this message]
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