genirq: Provide irq_enter/exit_rcu()

irq_enter()/exit() currently include RCU handling. To properly separate the RCU
handling code, provide variants which contain only the non-RCU related
functionality.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202117.567023613@linutronix.de

kernel/softirq.c

@@ -339,12 +339,11 @@ asmlinkage __visible void do_softirq(void)
 	local_irq_restore(flags);
 }
 
-/*
- * Enter an interrupt context.
+/**
+ * irq_enter_rcu - Enter an interrupt context with RCU watching
  */
-void irq_enter(void)
+void irq_enter_rcu(void)
 {
-	rcu_irq_enter();
 	if (is_idle_task(current) && !in_interrupt()) {
 		/*
 		 * Prevent raise_softirq from needlessly waking up ksoftirqd
@@ -354,10 +353,18 @@ void irq_enter(void)
 		tick_irq_enter();
 		_local_bh_enable();
 	}
-
 	__irq_enter();
 }
 
+/**
+ * irq_enter - Enter an interrupt context including RCU update
+ */
+void irq_enter(void)
+{
+	rcu_irq_enter();
+	irq_enter_rcu();
+}
+
 static inline void invoke_softirq(void)
 {
 	if (ksoftirqd_running(local_softirq_pending()))
@@ -397,10 +404,12 @@ static inline void tick_irq_exit(void)
 #endif
 }
 
-/*
- * Exit an interrupt context. Process softirqs if needed and possible:
+/**
+ * irq_exit_rcu() - Exit an interrupt context without updating RCU
+ *
+ * Also processes softirqs if needed and possible.
  */
-void irq_exit(void)
+void irq_exit_rcu(void)
 {
 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 	local_irq_disable();
@@ -413,6 +422,16 @@ void irq_exit(void)
 		invoke_softirq();
 
 	tick_irq_exit();
+}
+
+/**
+ * irq_exit - Exit an interrupt context, update RCU and lockdep
+ *
+ * Also processes softirqs if needed and possible.
+ */
+void irq_exit(void)
+{
+	irq_exit_rcu();
 	rcu_irq_exit();
 	 /* must be last! */
 	lockdep_hardirq_exit();