Messages in this thread | | | From | Nuno Gonçalves <> | Date | Mon, 5 Oct 2015 16:10:28 +0100 | Subject | Re: [tip:timers/urgent] time: Fix timekeeping_freqadjust()' s incorrect use of abs() instead of abs64() |
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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).
Thanks, Nuno
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