Re: /proc/kcore has a unreasonable size(281474974617600) in x86_642.6.30-rc8.

[Tao Ma]

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@xxxxxxxxx> writes:
>
> > On Mon, Jun 08, 2009 at 09:10:10PM -0700, Eric W. Biederman wrote:
> > > AmÃrico Wang <xiyou.wangcong@xxxxxxxxx> writes:
> > >
> > > > On Mon, Jun 8, 2009 at 4:00 PM, Tao Ma<tao.ma@xxxxxxxxxx> 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@ocfs2-test2 ~]$ dmesg|grep "high memory"
> > > > > high memory ffff88013c000000, size 5301604352
> > > > > [taoma@ocfs2-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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