rcu: Create directory for each flavor of rcu

This patch will create subdirectory according to each flavor of rcu, the new
structure will be:

	/debugfs/rcu/ -> rsp_0
		      -> rsp_1
		      -> ...

So we can go to '/debugfs/rcu/rsp_0' and get the cpu info of rsp_0 there.
The flavors of RCU are currently rcu_bh, rcu_preempt, and rcu_sched.
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree_trace.c

@@ -446,12 +446,20 @@ static struct dentry *rcudir;
 
 static int __init rcutree_trace_init(void)
 {
+	struct rcu_state *rsp;
 	struct dentry *retval;
+	struct dentry *rspdir;
 
 	rcudir = debugfs_create_dir("rcu", NULL);
 	if (!rcudir)
 		goto free_out;
 
+	for_each_rcu_flavor(rsp) {
+		rspdir = debugfs_create_dir(rsp->name, rcudir);
+		if (!rspdir)
+			goto free_out;
+	}
+
 	retval = debugfs_create_file("rcubarrier", 0444, rcudir,
 						NULL, &rcubarrier_fops);
 	if (!retval)