rcu: Use smp_hotplug_thread facility for RCUs per-CPU kthread

Bring RCU into the new-age CPU-hotplug fold by modifying RCU's per-CPU
kthread code to use the new smp_hotplug_thread facility.

[ tglx: Adapted it to use callbacks and to the simplified rcu yield ]
    
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20120716103948.673354828@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index abffb48..3196893 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -108,11 +108,10 @@
 			rdp->nxttail[RCU_WAIT_TAIL]],
 		   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
 #ifdef CONFIG_RCU_BOOST
-	seq_printf(m, " kt=%d/%c/%d ktl=%x",
+	seq_printf(m, " kt=%d/%c ktl=%x",
 		   per_cpu(rcu_cpu_has_work, rdp->cpu),
 		   convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
 					  rdp->cpu)),
-		   per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
 		   per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff);
 #endif /* #ifdef CONFIG_RCU_BOOST */
 	seq_printf(m, " b=%ld", rdp->blimit);