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

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Date:	Wed, 22 Oct 2008 12:39:07 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Alexey Dobriyan <adobriyan@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/proc: fix /proc/cpuinfo cpu offline bug


Hi, Ingo and Alexey,

I have changed my changelog. please review again.

Thanks, Lai.

Lai Jiangshan wrote:
> On Fri, Oct 17, 2008 at 7:41 PM, Alexey Dobriyan <adobriyan@...il.com> wrote:
>> 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?
> 
> this is not wrong /proc/cpuinfo, this is an enlarged /proc/cpuinfo
> this trivial example just use "show bug\n" as the enlarged content.
> 
> if you boot your machine with enough cpu, your /proc/cpuinfo
> have been enlarged too, please use this:
> 
> #!/bin/sh
> nr_cpus=16 #  i386
> for ((i=1; i<nr_cpus; i++))
> do
>     echo 0 > /sys/devices/system/cpu/cpu$i/online
>     cpus=$(grep processor /proc/cpuinfo | wc -l)
>     (( cpus == nr_cpus -1 )) || break; # bug eccur
>     echo 1 > /sys/devices/system/cpu/cpu$i/online
> done
> cat /proc/cpuinfo  # it shows this bug.
> 
> Lai
> 
>>> 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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> 
> 
> 


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