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 <johnstul@us.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Link: http://lkml.kernel.org/r/1342156917-25092-8-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files 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