Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull NOHZ fix from Ingo Molnar:
 "This fixes an old NOHZ race where we incorrectly calculate the next
  timer interrupt in certain circumstances where hrtimers are pending,
  that can cause hard to reproduce stalled-values artifacts in
  /proc/stat"

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  nohz: Fix collision between tick and other hrtimers

2 files changed, 9 insertions, 2 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 2c115fdab397..74e0388cc88d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -767,7 +767,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
         tick = expires;
 
         /* Skip reprogram of event if its not changed */
-        if (ts->tick_stopped && (expires == dev->next_event))
+        if (ts->tick_stopped && (expires == ts->next_tick))
                 goto out;
 
         /*
@@ -787,6 +787,8 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
                 trace_tick_stop(1, TICK_DEP_MASK_NONE);
         }
 
+        ts->next_tick = tick;
+
         /*
          * If the expiration time == KTIME_MAX, then we simply stop
          * the tick timer.
@@ -802,7 +804,10 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
         else
                 tick_program_event(tick, 1);
 out:
-        /* Update the estimated sleep length */
+        /*
+         * Update the estimated sleep length until the next timer
+         * (not only the tick).
+         */
         ts->sleep_length = ktime_sub(dev->next_event, now);
         return tick;
 }
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index bf38226e5c17..075444e3d48e 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -27,6 +27,7 @@ enum tick_nohz_mode {
  *                      timer is modified for nohz sleeps. This is necessary
  *                      to resume the tick timer operation in the timeline
  *                      when the CPU returns from nohz sleep.
+ * @next_tick:          Next tick to be fired when in dynticks mode.
  * @tick_stopped:       Indicator that the idle tick has been stopped
  * @idle_jiffies:       jiffies at the entry to idle for idle time accounting
  * @idle_calls:         Total number of idle calls
@@ -44,6 +45,7 @@ struct tick_sched {
         unsigned long                   check_clocks;
         enum tick_nohz_mode             nohz_mode;
         ktime_t                         last_tick;
+        ktime_t                         next_tick;
         int                             inidle;
         int                             tick_stopped;
         unsigned long                   idle_jiffies;