include/linux/timekeeper_internal.h |  1 +
 kernel/time/timekeeping.c           | 25 ++++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index 05af9a334893..0fcb60d77079 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -32,6 +32,7 @@ struct tk_read_base {
 	cycle_t			(*read)(struct clocksource *cs);
 	cycle_t			mask;
 	cycle_t			cycle_last;
+	cycle_t			cycle_error;
 	u32			mult;
 	u32			shift;
 	u64			xtime_nsec;
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6a931852082f..1c842ddd567f 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -140,6 +140,7 @@ static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock)
 	tk->tkr.read = clock->read;
 	tk->tkr.mask = clock->mask;
 	tk->tkr.cycle_last = tk->tkr.read(clock);
+	tk->tkr.cycle_error = 0;
 
 	/* Do the ns -> cycle conversion first, using original mult */
 	tmp = NTP_INTERVAL_LENGTH;
@@ -197,11 +198,17 @@ static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
 	s64 nsec;
 
 	/* read clocksource: */
-	cycle_now = tkr->read(tkr->clock);
+	cycle_now = tkr->read(tkr->clock) + tkr->cycle_error;
 
 	/* calculate the delta since the last update_wall_time: */
 	delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);
 
+	/* Hmm? This is really not good, we're too close to overflowing */
+	if (unlikely(delta > (tkr->mask >> 3))) {
+		tkr->cycle_error = delta;
+		delta = 0;
+	}
+
 	nsec = delta * tkr->mult + tkr->xtime_nsec;
 	nsec >>= tkr->shift;
 
@@ -465,6 +472,16 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action)
 	update_fast_timekeeper(tk);
 }
 
+static void check_cycle_error(struct tk_read_base *tkr)
+{
+	cycle_t error = tkr->cycle_error;
+
+	if (unlikely(error)) {
+		tkr->cycle_error = 0;
+		pr_err("Clocksource %s had cycles off by %llu\n", tkr->clock->name, error);
+	}
+}
+
 /**
  * timekeeping_forward_now - update clock to the current time
  *
@@ -481,6 +498,7 @@ static void timekeeping_forward_now(struct timekeeper *tk)
 	cycle_now = tk->tkr.read(clock);
 	delta = clocksource_delta(cycle_now, tk->tkr.cycle_last, tk->tkr.mask);
 	tk->tkr.cycle_last = cycle_now;
+	check_cycle_error(&tk->tkr);
 
 	tk->tkr.xtime_nsec += delta * tk->tkr.mult;
 
@@ -1237,6 +1255,7 @@ static void timekeeping_resume(void)
 
 	/* Re-base the last cycle value */
 	tk->tkr.cycle_last = cycle_now;
+	tk->tkr.cycle_error = 0;
 	tk->ntp_error = 0;
 	timekeeping_suspended = 0;
 	timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
@@ -1591,11 +1610,15 @@ void update_wall_time(void)
 	if (unlikely(timekeeping_suspended))
 		goto out;
 
+	check_cycle_error(&real_tk->tkr);
+
 #ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
 	offset = real_tk->cycle_interval;
 #else
 	offset = clocksource_delta(tk->tkr.read(tk->tkr.clock),
 				   tk->tkr.cycle_last, tk->tkr.mask);
+	if (unlikely(offset > (tk->tkr.mask >> 3)))
+		pr_err("Cutting it too close for %s in in update_wall_time (offset = %llu)\n", tk->tkr.clock->name, offset);
 #endif
 
 	/* Check if there's really nothing to do */