rcu: Add tracing for synchronize_sched_expedited()

This commit adds a per-RCU-flavor "rcuexp" file that dumps out
statistics for synchonize_sched_expedited().
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree_trace.c

@@ -173,6 +173,38 @@ static const struct file_operations rcudata_fops = {
 	.release = seq_release,
 };
 
+static int show_rcuexp(struct seq_file *m, void *v)
+{
+	struct rcu_state *rsp = (struct rcu_state *)m->private;
+
+	seq_printf(m, "s=%lu d=%lu w=%lu tf=%lu wd1=%lu wd2=%lu n=%lu sc=%lu dt=%lu dl=%lu dx=%lu\n",
+		   atomic_long_read(&rsp->expedited_start),
+		   atomic_long_read(&rsp->expedited_done),
+		   atomic_long_read(&rsp->expedited_wrap),
+		   atomic_long_read(&rsp->expedited_tryfail),
+		   atomic_long_read(&rsp->expedited_workdone1),
+		   atomic_long_read(&rsp->expedited_workdone2),
+		   atomic_long_read(&rsp->expedited_normal),
+		   atomic_long_read(&rsp->expedited_stoppedcpus),
+		   atomic_long_read(&rsp->expedited_done_tries),
+		   atomic_long_read(&rsp->expedited_done_lost),
+		   atomic_long_read(&rsp->expedited_done_exit));
+	return 0;
+}
+
+static int rcuexp_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, show_rcuexp, inode->i_private);
+}
+
+static const struct file_operations rcuexp_fops = {
+	.owner = THIS_MODULE,
+	.open = rcuexp_open,
+	.read = seq_read,
+	.llseek = no_llseek,
+	.release = seq_release,
+};
+
 #ifdef CONFIG_RCU_BOOST
 
 static void print_one_rcu_node_boost(struct seq_file *m, struct rcu_node *rnp)
@@ -405,6 +437,11 @@ static int __init rcutree_trace_init(void)
 		if (!retval)
 			goto free_out;
 
+		retval = debugfs_create_file("rcuexp", 0444,
+				rspdir, rsp, &rcuexp_fops);
+		if (!retval)
+			goto free_out;
+
 		retval = debugfs_create_file("rcu_pending", 0444,
 				rspdir, rsp, &rcu_pending_fops);
 		if (!retval)