rcu: Define rcu_all_qs() only in !PREEMPT builds

Now that rcu_all_qs() is used only in !PREEMPT builds, move it to
tree_plugin.h so that it is defined only in those builds.  This in
turn means that rcu_momentary_dyntick_idle() is only used in !PREEMPT
builds, but it is simply marked __maybe_unused in order to keep it
near the rest of the dyntick-idle code.

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

include/linux/rcutree.h

@@ -66,7 +66,9 @@ void rcu_scheduler_starting(void);
 extern int rcu_scheduler_active __read_mostly;
 void rcu_end_inkernel_boot(void);
 bool rcu_is_watching(void);
+#ifndef CONFIG_PREEMPT
 void rcu_all_qs(void);
+#endif
 
 /* RCUtree hotplug events */
 int rcutree_prepare_cpu(unsigned int cpu);

kernel/rcu/tree.c

@@ -356,7 +356,7 @@ bool rcu_eqs_special_set(int cpu)
  *
  * The caller must have disabled interrupts and must not be idle.
  */
-static void rcu_momentary_dyntick_idle(void)
+static void __maybe_unused rcu_momentary_dyntick_idle(void)
 {
 	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
 	int special;
@@ -381,45 +381,6 @@ static int rcu_is_cpu_rrupt_from_idle(void)
 	       __this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1;
 }
 
-/*
- * Register an urgently needed quiescent state.  If there is an
- * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
- * dyntick-idle quiescent state visible to other CPUs, which will in
- * some cases serve for expedited as well as normal grace periods.
- * Either way, register a lightweight quiescent state.
- *
- * The barrier() calls are redundant in the common case when this is
- * called externally, but just in case this is called from within this
- * file.
- *
- */
-void rcu_all_qs(void)
-{
-	unsigned long flags;
-
-	if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
-		return;
-	preempt_disable();
-	/* Load rcu_urgent_qs before other flags. */
-	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
-		preempt_enable();
-		return;
-	}
-	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
-	barrier(); /* Avoid RCU read-side critical sections leaking down. */
-	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
-		local_irq_save(flags);
-		rcu_momentary_dyntick_idle();
-		local_irq_restore(flags);
-	}
-	if (unlikely(raw_cpu_read(rcu_data.cpu_no_qs.b.exp)))
-		rcu_qs();
-	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
-	barrier(); /* Avoid RCU read-side critical sections leaking up. */
-	preempt_enable();
-}
-EXPORT_SYMBOL_GPL(rcu_all_qs);
-
 #define DEFAULT_RCU_BLIMIT 10     /* Maximum callbacks per rcu_do_batch. */
 static long blimit = DEFAULT_RCU_BLIMIT;
 #define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */

kernel/rcu/tree_plugin.h

@@ -947,6 +947,45 @@ static void rcu_qs(void)
 	rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
 }
 
+/*
+ * Register an urgently needed quiescent state.  If there is an
+ * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
+ * dyntick-idle quiescent state visible to other CPUs, which will in
+ * some cases serve for expedited as well as normal grace periods.
+ * Either way, register a lightweight quiescent state.
+ *
+ * The barrier() calls are redundant in the common case when this is
+ * called externally, but just in case this is called from within this
+ * file.
+ *
+ */
+void rcu_all_qs(void)
+{
+	unsigned long flags;
+
+	if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
+		return;
+	preempt_disable();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
+		preempt_enable();
+		return;
+	}
+	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
+	barrier(); /* Avoid RCU read-side critical sections leaking down. */
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
+		local_irq_save(flags);
+		rcu_momentary_dyntick_idle();
+		local_irq_restore(flags);
+	}
+	if (unlikely(raw_cpu_read(rcu_data.cpu_no_qs.b.exp)))
+		rcu_qs();
+	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
+	barrier(); /* Avoid RCU read-side critical sections leaking up. */
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(rcu_all_qs);
+
 /*
  * Note a PREEMPT=n context switch.  The caller must have disabled interrupts.
  */