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.
CC: Ingo Molnar <mi...@kernel.org>
CC: Peter Zijlstra <a.p.zijls...@chello.nl>
CC: Richard Cochran <richardcoch...@gmail.com>
CC: Prarit Bhargava <pra...@redhat.com>
CC: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: John Stultz <johns...@us.ibm.com>
---
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 dd119355..4b76432 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -987,6 +987,27 @@ 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;
+ }
+
}
@@ -1112,27 +1133,6 @@ 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
--
1.7.9.5
--
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