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Date: Tue, 26 Jul 2011 18:34:24 +0200
From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        kobayashi.kk@ncos.nec.co.jp
Subject: Re: [PATCH] proc/softirqs: only show state for online cpus
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On Tue, Jul 26, 2011 at 03:29:43PM +0800, Yong Zhang wrote:
> > Offtopic, /proc/interrupt should be protected by get_online_cpus().
> > Otherwise the header (i.e. cpu number) and the actual statistics fields
> > can be mismatched likes following. Am I missing something?
> 
> I think you are right. The reader could be preempted by cpu hotplug.
> 
> After searching the whole tree, only s390 take cpu_hotplug.lock,
> but its usage is not currect:
> 
> arch/s390/kernel/irq.c:
> int show_interrupts(struct seq_file *p, void *v)
> {
>           get_online_cpus();
>           .........
>           put_online_cpus();
> }
> 
> Because the reader will call show_interrupts nr_irqs times.
> So get_online_cpus()/put_online_cpus() should be put upper,
> maybe interrupts_open(). How do you think about it?

Indeed, it's broken. You're going to submit a patch?