linux-kernel - Re: [PATCH 4/9] s390/irq: utilize RCU instead of irq_lock_sparse() in show_msi

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Date:   Fri, 22 Apr 2022 17:56:37 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] s390/irq: utilize RCU instead of irq_lock_sparse()
 in show_msi_interrupt()

On Thu, Apr 21, 2022 at 01:42:59PM +0200, Heiko Carstens wrote:
> On Thu, Apr 21, 2022 at 11:36:17AM +0800, Pingfan Liu wrote:
> > Oops. You are right. What about using rcu_read_lock() directly?
> > 
> > 
> > diff --git a/arch/s390/kernel/irq.c b/arch/s390/kernel/irq.c
> > index 3033f616e256..45393919fe61 100644
> > --- a/arch/s390/kernel/irq.c
> > +++ b/arch/s390/kernel/irq.c
> > @@ -205,7 +205,7 @@ static void show_msi_interrupt(struct seq_file *p, int irq)
> >  	unsigned long flags;
> >  	int cpu;
> >  
> > -	irq_lock_sparse();
> > +	rcu_read_lock();
> >  	desc = irq_to_desc(irq);
> >  	if (!desc)
> >  		goto out;
> > @@ -224,7 +224,7 @@ 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();
> > +	rcu_read_unlock();
> 
> That looks like it should work. Please resend and also add a reference
> to commit 74bdf7815dfb ("genirq: Speedup show_interrupts()") which
> explains why this works.

Thanks for your review. I will follow up with V2.

Regards,

	Pingfan