rcu/nocb: Remove obsolete nocb_q_count and nocb_q_count_lazy fields

This commit removes the obsolete nocb_q_count and nocb_q_count_lazy
fields, also removing rcu_get_n_cbs_nocb_cpu(), adjusting
rcu_get_n_cbs_cpu(), and making rcutree_migrate_callbacks() once again
disable the ->cblist fields of offline CPUs.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/tree.c

@@ -210,10 +210,9 @@ static long rcu_get_n_cbs_cpu(int cpu)
 {
 	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 
-	if (rcu_segcblist_is_enabled(&rdp->cblist) &&
-	    !rcu_segcblist_is_offloaded(&rdp->cblist)) /* Online normal CPU? */
+	if (rcu_segcblist_is_enabled(&rdp->cblist))
 		return rcu_segcblist_n_cbs(&rdp->cblist);
-	return rcu_get_n_cbs_nocb_cpu(rdp); /* Works for offline, too. */
+	return 0;
 }
 
 void rcu_softirq_qs(void)
@@ -3181,6 +3180,7 @@ void rcutree_migrate_callbacks(int cpu)
 	needwake = rcu_advance_cbs(my_rnp, rdp) ||
 		   rcu_advance_cbs(my_rnp, my_rdp);
 	rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
+	rcu_segcblist_disable(&rdp->cblist);
 	WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
 		     !rcu_segcblist_n_cbs(&my_rdp->cblist));
 	if (rcu_segcblist_is_offloaded(&my_rdp->cblist)) {

kernel/rcu/tree.h

@@ -194,8 +194,6 @@ struct rcu_data {
 
 	/* 5) Callback offloading. */
 #ifdef CONFIG_RCU_NOCB_CPU
-	atomic_long_t nocb_q_count;	/* # CBs waiting for nocb */
-	atomic_long_t nocb_q_count_lazy; /*  invocation (all stages). */
 	struct rcu_head *nocb_cb_head;	/* CBs ready to invoke. */
 	struct rcu_head **nocb_cb_tail;
 	struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
@@ -437,7 +435,6 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
 #ifdef CONFIG_RCU_NOCB_CPU
 static void __init rcu_organize_nocb_kthreads(void);
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
-static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp);
 static void rcu_bind_gp_kthread(void);
 static bool rcu_nohz_full_cpu(void);
 static void rcu_dynticks_task_enter(void);

kernel/rcu/tree_plugin.h

@@ -2040,15 +2040,6 @@ void rcu_bind_current_to_nocb(void)
 }
 EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
 
-/*
- * Return the number of RCU callbacks still queued from the specified
- * CPU, which must be a nocbs CPU.
- */
-static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp)
-{
-	return atomic_long_read(&rdp->nocb_q_count);
-}
-
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 
 /* No ->nocb_lock to acquire.  */
@@ -2108,11 +2099,6 @@ static void __init rcu_spawn_nocb_kthreads(void)
 {
 }
 
-static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp)
-{
-	return 0;
-}
-
 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 
 /*