s390/entry: fix duplicate tracking of irq nesting level

In the current code, when exiting from idle, rcu_irq_enter() is
called twice during irq entry:

irq_entry_enter()-> rcu_irq_enter()
irq_enter() -> rcu_irq_enter()

This may lead to wrong results from rcu_is_cpu_rrupt_from_idle()
because of a wrong dynticks nmi nesting count. Fix this by only
calling irq_enter_rcu().

Cc: <stable@vger.kernel.org> # 5.12+
Reported-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 56e62a7 ("s390: convert to generic entry")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/irq.c

@@ -138,7 +138,7 @@ void noinstr do_io_irq(struct pt_regs *regs)
 	struct pt_regs *old_regs = set_irq_regs(regs);
 	int from_idle;
 
-	irq_enter();
+	irq_enter_rcu();
 
 	if (user_mode(regs)) {
 		update_timer_sys();
@@ -158,7 +158,8 @@ void noinstr do_io_irq(struct pt_regs *regs)
 			do_irq_async(regs, IO_INTERRUPT);
 	} while (MACHINE_IS_LPAR && irq_pending(regs));
 
-	irq_exit();
+	irq_exit_rcu();
+
 	set_irq_regs(old_regs);
 	irqentry_exit(regs, state);
 
@@ -172,7 +173,7 @@ void noinstr do_ext_irq(struct pt_regs *regs)
 	struct pt_regs *old_regs = set_irq_regs(regs);
 	int from_idle;
 
-	irq_enter();
+	irq_enter_rcu();
 
 	if (user_mode(regs)) {
 		update_timer_sys();
@@ -190,7 +191,7 @@ void noinstr do_ext_irq(struct pt_regs *regs)
 
 	do_irq_async(regs, EXT_INTERRUPT);
 
-	irq_exit();
+	irq_exit_rcu();
 	set_irq_regs(old_regs);
 	irqentry_exit(regs, state);