In tc_windup, handle the case where the previous call to tc_windup was

more than 1s earlier.  Prior to this commit, the computation of
th_scale * delta (which produces a 64-bit value equal to the time since
the last tc_windup call in units of 2^(-64) seconds) would overflow and
any complete seconds would be lost.

We fix this by repeatedly converting tc_frequency units of timecounter
to one seconds; this is not exactly correct, since it loses the NTP
adjustment, but if we find ourselves going more than 1s at a time between
clock interrupts, losing a few seconds worth of NTP adjustments is the
least of our problems...

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index 3e8d470..2487b6b 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -442,6 +442,16 @@ tc_windup(void)
 		ncount = 0;
 	th->th_offset_count += delta;
 	th->th_offset_count &= th->th_counter->tc_counter_mask;
+	while (delta > th->th_counter->tc_frequency) {
+		/* Eat complete unadjusted seconds. */
+		delta -= th->th_counter->tc_frequency;
+		th->th_offset.sec++;
+	}
+	if ((delta > th->th_counter->tc_frequency / 2) &&
+	    (th->th_scale * delta < (uint64_t)1 << 63)) {
+		/* The product th_scale * delta just barely overflows. */
+		th->th_offset.sec++;
+	}
 	bintime_addx(&th->th_offset, th->th_scale * delta);
 
 	/*