From 2a8c0883c3cfffcc148ea606e2a4e7453cd75e73 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Fri, 13 Jul 2012 01:21:56 -0400 Subject: [PATCH] time: Move xtime_nsec adjustment underflow handling timekeeping_adjust When we make adjustments speeding up the clock, its possible for xtime_nsec to underflow. We already handle this properly, but we do so from update_wall_time() instead of the more logical timekeeping_adjust(), where the possible underflow actually occurs. Thus, move the correction logic to the timekeeping_adjust, which is the function that causes the issue. Making update_wall_time() more readable. Signed-off-by: John Stultz Reviewed-by: Ingo Molnar Cc: Peter Zijlstra Cc: Richard Cochran Cc: Prarit Bhargava Link: http://lkml.kernel.org/r/1342156917-25092-8-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner --- kernel/time/timekeeping.c | 42 +++++++++++++++++++-------------------- 1 file changed, 21 insertions(+), 21 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index e43289df28c2..aeeaab8cba6e 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -980,6 +980,27 @@ static void timekeeping_adjust(s64 offset) timekeeper.xtime_nsec -= offset; timekeeper.ntp_error -= (interval - offset) << timekeeper.ntp_error_shift; + + /* + * It may be possible that when we entered this function, xtime_nsec + * was very small. Further, if we're slightly speeding the clocksource + * in the code above, its possible the required corrective factor to + * xtime_nsec could cause it to underflow. + * + * Now, since we already accumulated the second, cannot simply roll + * the accumulated second back, since the NTP subsystem has been + * notified via second_overflow. So instead we push xtime_nsec forward + * by the amount we underflowed, and add that amount into the error. + * + * We'll correct this error next time through this function, when + * xtime_nsec is not as small. + */ + if (unlikely((s64)timekeeper.xtime_nsec < 0)) { + s64 neg = -(s64)timekeeper.xtime_nsec; + timekeeper.xtime_nsec = 0; + timekeeper.ntp_error += neg << timekeeper.ntp_error_shift; + } + } @@ -1105,27 +1126,6 @@ static void update_wall_time(void) /* correct the clock when NTP error is too big */ timekeeping_adjust(offset); - /* - * Since in the loop above, we accumulate any amount of time - * in xtime_nsec over a second into xtime.tv_sec, its possible for - * xtime_nsec to be fairly small after the loop. Further, if we're - * slightly speeding the clocksource up in timekeeping_adjust(), - * its possible the required corrective factor to xtime_nsec could - * cause it to underflow. - * - * Now, we cannot simply roll the accumulated second back, since - * the NTP subsystem has been notified via second_overflow. So - * instead we push xtime_nsec forward by the amount we underflowed, - * and add that amount into the error. - * - * We'll correct this error next time through this function, when - * xtime_nsec is not as small. - */ - if (unlikely((s64)timekeeper.xtime_nsec < 0)) { - s64 neg = -(s64)timekeeper.xtime_nsec; - timekeeper.xtime_nsec = 0; - timekeeper.ntp_error += neg << timekeeper.ntp_error_shift; - } /* * Store only full nanoseconds into xtime_nsec after rounding -- 2.30.2