2 files changed, 47 insertions, 18 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 502a81e2639b..8f3fc2582d38 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -247,7 +247,7 @@ void tick_nohz_stop_sched_tick(int inidle)
         if (need_resched())
                 goto end;
 
-        if (unlikely(local_softirq_pending())) {
+        if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
                 static int ratelimit;
 
                 if (ratelimit < 10) {
@@ -282,8 +282,31 @@ void tick_nohz_stop_sched_tick(int inidle)
         /* Schedule the tick, if we are at least one jiffie off */
         if ((long)delta_jiffies >= 1) {
 
+                /*
+                * calculate the expiry time for the next timer wheel
+                * timer
+                */
+                expires = ktime_add_ns(last_update, tick_period.tv64 *
+                                   delta_jiffies);
+
+                /*
+                 * If this cpu is the one which updates jiffies, then
+                 * give up the assignment and let it be taken by the
+                 * cpu which runs the tick timer next, which might be
+                 * this cpu as well. If we don't drop this here the
+                 * jiffies might be stale and do_timer() never
+                 * invoked.
+                 */
+                if (cpu == tick_do_timer_cpu)
+                        tick_do_timer_cpu = TICK_DO_TIMER_NONE;
+
                 if (delta_jiffies > 1)
                         cpu_set(cpu, nohz_cpu_mask);
+
+                /* Skip reprogram of event if its not changed */
+                if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
+                        goto out;
+
                 /*
                  * nohz_stop_sched_tick can be called several times before
                  * the nohz_restart_sched_tick is called. This happens when
@@ -306,17 +329,6 @@ void tick_nohz_stop_sched_tick(int inidle)
                         rcu_enter_nohz();
                 }
 
-                /*
-                 * If this cpu is the one which updates jiffies, then
-                 * give up the assignment and let it be taken by the
-                 * cpu which runs the tick timer next, which might be
-                 * this cpu as well. If we don't drop this here the
-                 * jiffies might be stale and do_timer() never
-                 * invoked.
-                 */
-                if (cpu == tick_do_timer_cpu)
-                        tick_do_timer_cpu = TICK_DO_TIMER_NONE;
-
                 ts->idle_sleeps++;
 
                 /*
@@ -332,12 +344,7 @@ void tick_nohz_stop_sched_tick(int inidle)
                         goto out;
                 }
 
-                /*
-                 * calculate the expiry time for the next timer wheel
-                 * timer
-                 */
-                expires = ktime_add_ns(last_update, tick_period.tv64 *
-                                       delta_jiffies);
+                /* Mark expiries */
                 ts->idle_expires = expires;
 
                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e7acfb482a68..fa05e88aa76f 100644
--- 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.
          */