On Sun, Sep 13, 2015 at 12:07 PM, tip-bot for John Stultz <tipbot@xxxxxxxxx> wrote: > Commit-ID: 2619d7e9c92d524cb155ec89fd72875321512e5b > Gitweb: http://git.kernel.org/tip/2619d7e9c92d524cb155ec89fd72875321512e5b > Author: John Stultz <john.stultz@xxxxxxxxxx> > AuthorDate: Wed, 9 Sep 2015 16:07:30 -0700 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > 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@xxxxxxxxx> > Tested-by: Nuno Goncalves <nunojpg@xxxxxxxxx> > Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> # v3.17+ > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: Miroslav Lichvar <mlichvar@xxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Prarit Bhargava <prarit@xxxxxxxxxx> > Cc: Richard Cochran <richardcochran@xxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Link: http://lkml.kernel.org/r/1441840051-20244-1-git-send-email-john.stultz@xxxxxxxxxx > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> > --- > 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html