linux-kernel - Re: [PATCH] proc/softirqs: only show state for online cpus

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Message-ID: <CAM2zO=BvgSeTiD16zVbb+3To418vkbZ3LEYzzsuZixZtEY-GSw@mail.gmail.com>
Date:	Wed, 27 Jul 2011 10:41:53 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	kobayashi.kk@...s.nec.co.jp
Subject: Re: [PATCH] proc/softirqs: only show state for online cpus

On Wed, Jul 27, 2011 at 12:34 AM, Heiko Carstens
<heiko.carstens@...ibm.com> wrote:
> 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?
>

Yeah, coming soon :)

Thanks,
Yong



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