[PATCH] NOHZ: Fix RCU handling

When a CPU is needed for RCU the tick has to continue even when it was
stopped before.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/time/tick-sched.c

@@ -191,19 +191,19 @@ void tick_nohz_stop_sched_tick(void)
 	next_jiffies = get_next_timer_interrupt(last_jiffies);
 	delta_jiffies = next_jiffies - last_jiffies;
 
+	if (rcu_needs_cpu(cpu))
+		delta_jiffies = 1;
 	/*
 	 * Do not stop the tick, if we are only one off
 	 * or if the cpu is required for rcu
 	 */
-	if (!ts->tick_stopped && (delta_jiffies == 1 || rcu_needs_cpu(cpu)))
+	if (!ts->tick_stopped && delta_jiffies == 1)
 		goto out;
 
 	/* Schedule the tick, if we are at least one jiffie off */
 	if ((long)delta_jiffies >= 1) {
 
-		if (rcu_needs_cpu(cpu))
-			delta_jiffies = 1;
-		else
+		if (delta_jiffies > 1)
 			cpu_set(cpu, nohz_cpu_mask);
 		/*
 		 * nohz_stop_sched_tick can be called several times before