rcu: Remove "cpu" argument to rcu_prepare_for_idle()

The "cpu" argument to rcu_prepare_for_idle() is always the current
CPU, so drop it.  This in turn allows two of the uses of "cpu" in
this function to be replaced with a this_cpu_ptr() and the third by
smp_processor_id(), replacing that of the call to rcu_prepare_for_idle().
Again, the anticipated cross-CPU uses of these functions has been replaced
by NO_HZ_FULL.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>

kernel/rcu/tree.c

@@ -531,7 +531,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
 		rdp = this_cpu_ptr(rsp->rda);
 		do_nocb_deferred_wakeup(rdp);
 	}
-	rcu_prepare_for_idle(smp_processor_id());
+	rcu_prepare_for_idle();
 	/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
 	smp_mb__before_atomic();  /* See above. */
 	atomic_inc(&rdtp->dynticks);

kernel/rcu/tree.h

@@ -580,7 +580,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
 static void __init rcu_spawn_boost_kthreads(void);
 static void rcu_prepare_kthreads(int cpu);
 static void rcu_cleanup_after_idle(int cpu);
-static void rcu_prepare_for_idle(int cpu);
+static void rcu_prepare_for_idle(void);
 static void rcu_idle_count_callbacks_posted(void);
 static void print_cpu_stall_info_begin(void);
 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);

kernel/rcu/tree_plugin.h

@@ -1531,7 +1531,7 @@ static void rcu_cleanup_after_idle(int cpu)
  * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
  * is nothing.
  */
-static void rcu_prepare_for_idle(int cpu)
+static void rcu_prepare_for_idle(void)
 {
 }
 
@@ -1666,12 +1666,12 @@ int rcu_needs_cpu(unsigned long *dj)
  *
  * The caller must have disabled interrupts.
  */
-static void rcu_prepare_for_idle(int cpu)
+static void rcu_prepare_for_idle(void)
 {
 #ifndef CONFIG_RCU_NOCB_CPU_ALL
 	bool needwake;
 	struct rcu_data *rdp;
-	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 	struct rcu_node *rnp;
 	struct rcu_state *rsp;
 	int tne;
@@ -1688,7 +1688,7 @@ static void rcu_prepare_for_idle(int cpu)
 		return;
 
 	/* If this is a no-CBs CPU, no callbacks, just return. */
-	if (rcu_is_nocb_cpu(cpu))
+	if (rcu_is_nocb_cpu(smp_processor_id()))
 		return;
 
 	/*
@@ -1712,7 +1712,7 @@ static void rcu_prepare_for_idle(int cpu)
 		return;
 	rdtp->last_accelerate = jiffies;
 	for_each_rcu_flavor(rsp) {
-		rdp = per_cpu_ptr(rsp->rda, cpu);
+		rdp = this_cpu_ptr(rsp->rda);
 		if (!*rdp->nxttail[RCU_DONE_TAIL])
 			continue;
 		rnp = rdp->mynode;