linux-kernel - Re: /proc/kcore has a unreasonable size(281474974617600) in x86

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Date:	Fri, 12 Jun 2009 15:54:46 +0800
From:	Tao Ma <tao.ma@...cle.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Amerigo Wang <xiyou.wangcong@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: /proc/kcore has a unreasonable size(281474974617600) in x86_64
 2.6.30-rc8.

Hi all,
	sorry for the delay. I am occupied by other stuff these days.

I just tried and the strange thing is that 2 same boxes(Dell optiplex 
745) with 2.6.29 kernel have different output. One is normal and one is 
wrong. So I am totally puzzled now

So Eric may be right(there is a memory stomp), but it does show sometimes.

Regards,
Tao

Eric W. Biederman wrote:
> Amerigo Wang <xiyou.wangcong@...il.com> writes:
> 
>> On Mon, Jun 08, 2009 at 09:10:10PM -0700, Eric W. Biederman wrote:
>>> Américo Wang <xiyou.wangcong@...il.com> writes:
>>>
>>>> On Mon, Jun 8, 2009 at 4:00 PM, Tao Ma<tao.ma@...cle.com> wrote:
>>>>>>> But the result is the same
>>>>>> Yes?
>>>>>> Your printk() shows kcore size is: 5301604352, and in your subject it is
>>>>>> 281474974617600...
>>>>>>
>>>>>> Or they happened in the same time?
>>>>> yes. the same box and the same linux version.
>>>>> A bit strange.
>>>>>
>>>>> [taoma@...s2-test2 ~]$ dmesg|grep "high memory"
>>>>> high memory ffff88013c000000, size 5301604352
>>>>> [taoma@...s2-test2 ~]$ ll /proc/kcore
>>>>> -r-------- 1 root root 281474974617600 Jun  8 15:20 /proc/kcore
>>>> Really weird...
>>>> They should be the same. This means we have some problem in our procfs.
>>>>
>>>> And, we have no problem on i386, I, myself, even can't reproduce this on my
>>>> x86_64 box...
>>>>
>>>> Drop Cc to x86 people, add some Cc to proc people. :)
>>>>
>>>> Eric, Alexey, any ideas?
>>>>
>>>> Tao, would you like to send us your .config? Thanks.
>>> Short of some strange patch applied I would guess that a non-sense /proc/kcore
>>> size is related to a kernel memory stomp, stepping on the high_memory variable.
>> Hello, Eric.
>>
>> I see the problem now, I think the documentation of /proc/kcore
>> is wrong, the size of kcore can be more than the size of physical
>> memory, because it also contains the info of kernel modules which
>> stay above the mapping of phy memory, see arch/x86/mm/init_64.c.
>>
>> What do you think?
> 
> I think that doesn't make any sense.
> 
> I was reading the code.
> 
> I smell a nasty problem somewhere.
> 
> Eric
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