rcu: Move rcu_cpu_kthread_status to rcu_data structure

Given that RCU has a perfectly good per-CPU rcu_data structure, most
per-CPU quantities should be stored there.

This commit therefore moves the rcu_cpu_kthread_status per-CPU variable
to the rcu_data structure.  This also makes this variable unconditionally
present, which should be acceptable given the memory reduction due to the
RCU flavor consolidation and also due to simplifications this will enable.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/tree.h

@@ -237,6 +237,8 @@ struct rcu_data {
 	/* 6) RCU priority boosting. */
 	struct task_struct *rcu_cpu_kthread_task;
 					/* rcuc per-CPU kthread or NULL. */
+	unsigned int rcu_cpu_kthread_status;
+					/* Running status for rcuc. */
 
 	/* 7) Diagnostic data, including RCU CPU stall warnings. */
 	unsigned int softirq_snap;	/* Snapshot of softirq activity. */
@@ -407,7 +409,6 @@ static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
 int rcu_dynticks_snap(struct rcu_data *rdp);
 
 #ifdef CONFIG_RCU_BOOST
-DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 DECLARE_PER_CPU(char, rcu_cpu_has_work);

kernel/rcu/tree_plugin.h

@@ -40,7 +40,6 @@
 /*
  * Control variables for per-CPU and per-rcu_node kthreads.
  */
-DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 DEFINE_PER_CPU(char, rcu_cpu_has_work);
 
@@ -1310,7 +1309,7 @@ static void invoke_rcu_callbacks_kthread(void)
 	if (__this_cpu_read(rcu_data.rcu_cpu_kthread_task) != NULL &&
 	    current != __this_cpu_read(rcu_data.rcu_cpu_kthread_task)) {
 		rcu_wake_cond(__this_cpu_read(rcu_data.rcu_cpu_kthread_task),
-			      __this_cpu_read(rcu_cpu_kthread_status));
+			      __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
 	}
 	local_irq_restore(flags);
 }
@@ -1383,7 +1382,7 @@ static void rcu_cpu_kthread_setup(unsigned int cpu)
 
 static void rcu_cpu_kthread_park(unsigned int cpu)
 {
-	per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+	per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
 }
 
 static int rcu_cpu_kthread_should_run(unsigned int cpu)
@@ -1398,7 +1397,7 @@ static int rcu_cpu_kthread_should_run(unsigned int cpu)
  */
 static void rcu_cpu_kthread(unsigned int cpu)
 {
-	unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
+	unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
 	char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
 	int spincnt;