nohz: fix wrong event handler after online an offlined cpu

On the tickless system(CONFIG_NO_HZ=y and CONFIG_HIGH_RES_TIMERS=n), after
I made an offlined cpu online, I found this cpu's event handler was
tick_handle_periodic, not tick_nohz_handler.

After debuging, I found this bug was caused by the wrong tick mode.  the
tick mode is not changed to NOHZ_MODE_INACTIVE when the cpu is offline.

This patch fixes this bug.

Signed-off-by: Miao Xie <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

include/linux/tick.h

@@ -74,10 +74,13 @@ extern struct tick_device *tick_get_device(int cpu);
 extern int tick_init_highres(void);
 extern int tick_program_event(ktime_t expires, int force);
 extern void tick_setup_sched_timer(void);
+# endif
+
+# if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
 extern void tick_cancel_sched_timer(int cpu);
 # else
 static inline void tick_cancel_sched_timer(int cpu) { }
-# endif /* HIGHRES */
+# endif
 
 # ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
 extern struct tick_device *tick_get_broadcast_device(void);

kernel/time/tick-sched.c

@@ -643,17 +643,21 @@ void tick_setup_sched_timer(void)
 		ts->nohz_mode = NOHZ_MODE_HIGHRES;
 #endif
 }
+#endif /* HIGH_RES_TIMERS */
 
+#if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
 void tick_cancel_sched_timer(int cpu)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 
+# ifdef CONFIG_HIGH_RES_TIMERS
 	if (ts->sched_timer.base)
 		hrtimer_cancel(&ts->sched_timer);
+# endif
 
 	ts->nohz_mode = NOHZ_MODE_INACTIVE;
 }
-#endif /* HIGH_RES_TIMERS */
+#endif
 
 /**
  * Async notification about clocksource changes