linux-kernel - Re: [PATCH] x86/proc: fix /proc/cpuinfo cpu offline bug

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Message-ID: <20081017114132.GA18994@x200.localdomain>
Date:	Fri, 17 Oct 2008 15:41:32 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/proc: fix /proc/cpuinfo cpu offline bug

On Fri, Oct 17, 2008 at 04:55:25PM +0800, Lai Jiangshan wrote:
> In my test, I found that if a cpu has been offline,
> the next cpus may not be shown in the /proc/cpuinfo.
> 
> trivially reproduce this bug:
> 
> 1) add these lines in the end of show_cpuinfo()
> 	if (m->size - m->count - 20 > 0)
> 		seq_printf(m, "%*s", (int)(m->size - m->count - 20), "show bug\n");

What is it?

Can you just show wrong /proc/cpuinfo ?

Can someone with at least 4-way box please do so?

> 3) offline cpu#1
> 4) cat /proc/cpuinfo
>    cpu#2 and cpu#3 .... cannot be shown in /proc/cpuinfo

> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -160,14 +160,16 @@ static void *c_start(struct seq_file *m, loff_t *pos)
>  {
>  	if (*pos == 0)	/* just in case, cpu 0 is not the first */
>  		*pos = first_cpu(cpu_online_map);
> -	if ((*pos) < nr_cpu_ids && cpu_online(*pos))
> +	else
> +		*pos = next_cpu_nr(*pos - 1, cpu_online_map);
> +	if ((*pos) < nr_cpu_ids)
>  		return &cpu_data(*pos);
>  	return NULL;
>  }
>  
>  static void *c_next(struct seq_file *m, void *v, loff_t *pos)
>  {
> -	*pos = next_cpu(*pos, cpu_online_map);
> +	(*pos)++;
>  	return c_start(m, pos);
>  }
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