rcu: Don't do reschedule unless in irq

Condition the set_need_resched() in rcu_irq_exit() on in_irq().  This
should be a no-op, because rcu_irq_exit() should only be called from irq.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree.c

@@ -421,8 +421,9 @@ void rcu_irq_exit(void)
 	WARN_ON_ONCE(rdtp->dynticks & 0x1);
 
 	/* If the interrupt queued a callback, get out of dyntick mode. */
-	if (__this_cpu_read(rcu_sched_data.nxtlist) ||
-	    __this_cpu_read(rcu_bh_data.nxtlist))
+	if (in_irq() &&
+	    (__this_cpu_read(rcu_sched_data.nxtlist) ||
+	     __this_cpu_read(rcu_bh_data.nxtlist)))
 		set_need_resched();
 }