[PATCH 4/9] s390/irq: utilize RCU instead of irq_lock_sparse() in show_msi_interrupt()

[Pingfan Liu <kernelfans@gmail.com>]

irq_desc can be accessed safely in RCU read section as demonstrated by
kstat_irqs_usr(). And raw_spin_lock_irqsave() context can provide a rcu
read section, which can be utilized to get rid of irq_lock_sparse().

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org
To: linux-s390@vger.kernel.org
---
 arch/s390/kernel/irq.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/s390/kernel/irq.c b/arch/s390/kernel/irq.c
index 3033f616e256..6302dc7874cf 100644
--- a/arch/s390/kernel/irq.c
+++ b/arch/s390/kernel/irq.c
@@ -205,12 +205,13 @@ static void show_msi_interrupt(struct seq_file *p, int irq)
 	unsigned long flags;
 	int cpu;
 
-	irq_lock_sparse();
+	raw_spin_lock_irqsave(&desc->lock, flags);
 	desc = irq_to_desc(irq);
-	if (!desc)
-		goto out;
+	if (!desc) {
+		raw_spin_unlock_irqrestore(&desc->lock, flags);
+		return;
+	}
 
-	raw_spin_lock_irqsave(&desc->lock, flags);
 	seq_printf(p, "%3d: ", irq);
 	for_each_online_cpu(cpu)
 		seq_printf(p, "%10u ", irq_desc_kstat_cpu(desc, cpu));
@@ -223,8 +224,6 @@ static void show_msi_interrupt(struct seq_file *p, int irq)
 
 	seq_putc(p, '\n');
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
-out:
-	irq_unlock_sparse();
 }
 
 /*
-- 
2.31.1