rcu: Remove rsp parameter from rcu_spawn_one_boost_kthread()

There now is only one rcu_state structure in a given build of the
Linux kernel, so there is no need to pass it as a parameter to RCU's
functions.  This commit therefore removes the rsp parameter from
rcu_spawn_one_boost_kthread().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.h

@@ -463,10 +463,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static void invoke_rcu_callbacks_kthread(void);
 static bool rcu_is_callbacks_kthread(void);
-#ifdef CONFIG_RCU_BOOST
-static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
-						 struct rcu_node *rnp);
-#endif /* #ifdef CONFIG_RCU_BOOST */
 static void __init rcu_spawn_boost_kthreads(void);
 static void rcu_prepare_kthreads(int cpu);
 static void rcu_cleanup_after_idle(void);

kernel/rcu/tree_plugin.h

@@ -1290,21 +1290,20 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
  * already exist.  We only create this kthread for preemptible RCU.
  * Returns zero if all is well, a negated errno otherwise.
  */
-static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
-				       struct rcu_node *rnp)
+static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 {
-	int rnp_index = rnp - &rsp->node[0];
+	int rnp_index = rnp - rcu_get_root();
 	unsigned long flags;
 	struct sched_param sp;
 	struct task_struct *t;
 
-	if (&rcu_state != rsp)
+	if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
 		return 0;
 
 	if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
 		return 0;
 
-	rsp->boost = 1;
+	rcu_state.boost = 1;
 	if (rnp->boost_kthread_task != NULL)
 		return 0;
 	t = kthread_create(rcu_boost_kthread, (void *)rnp,
@@ -1430,7 +1429,7 @@ static void __init rcu_spawn_boost_kthreads(void)
 		per_cpu(rcu_cpu_has_work, cpu) = 0;
 	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
 	rcu_for_each_leaf_node(&rcu_state, rnp)
-		(void)rcu_spawn_one_boost_kthread(&rcu_state, rnp);
+		(void)rcu_spawn_one_boost_kthread(rnp);
 }
 
 static void rcu_prepare_kthreads(int cpu)
@@ -1440,7 +1439,7 @@ static void rcu_prepare_kthreads(int cpu)
 
 	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
 	if (rcu_scheduler_fully_active)
-		(void)rcu_spawn_one_boost_kthread(&rcu_state, rnp);
+		(void)rcu_spawn_one_boost_kthread(rnp);
 }
 
 #else /* #ifdef CONFIG_RCU_BOOST */