[GIT pull] timer fix for 4.15

[Thomas Gleixner]

Linus,

please pull the latest timers-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
timers-urgent-for-linus

A single fix for a ~10 years old problem which causes high resolution
timers to stop after a CPU unplug/plug cycle due to a stale flag in the per
CPU hrtimer base struct. Paul McKenney was hunting this for about a year,
but the heisenbug nature made it resistant against debug attempts for quite
some time.

Thanks,

        tglx

------------------>
Thomas Gleixner (1):
      hrtimer: Reset hrtimer cpu base proper on CPU hotplug


 kernel/time/hrtimer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index d32520840fde..aa9d2a2b1210 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -655,7 +655,9 @@ static void hrtimer_reprogram(struct hrtimer *timer,
 static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base)
 {
        base->expires_next = KTIME_MAX;
+       base->hang_detected = 0;
        base->hres_active = 0;
+       base->next_timer = NULL;
 }
 
 /*
@@ -1589,6 +1591,7 @@ int hrtimers_prepare_cpu(unsigned int cpu)
                timerqueue_init_head(&cpu_base->clock_base[i].active);
        }
 
+       cpu_base->active_bases = 0;
        cpu_base->cpu = cpu;
        hrtimer_init_hres(cpu_base);
        return 0;