Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-rc-fixes-2.6

[linux-2.6-omap-h63xx.git] / kernel / time / timekeeping.c

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e7acfb482a680ea248f5268fbb7f158868938e56..fa05e88aa76f36af2dc5cb0cc26f737466d0a423 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -518,6 +518,28 @@ void update_wall_time(void)
        /* correct the clock when NTP error is too big */
        clocksource_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 clocksource_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)clock->xtime_nsec < 0)) {
+               s64 neg = -(s64)clock->xtime_nsec;
+               clock->xtime_nsec = 0;
+               clock->error += neg << (NTP_SCALE_SHIFT - clock->shift);
+       }
+
        /* store full nanoseconds into xtime after rounding it up and
         * add the remainder to the error difference.
         */