linux-kernel - Re: [2.6.27] overlapping early reservations [was: early exception

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Date:	Sat, 6 Sep 2008 19:20:30 +0200
From:	"Luca Tettamanti" <kronos.it@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...nel.org>,
	"Peter Zijlstra" <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...hat.com
Subject: Re: [2.6.27] overlapping early reservations [was: early exception - lockdep related?]

On Sat, Sep 6, 2008 at 4:51 PM, Ingo Molnar <mingo@...e.hu> wrote:
> * Luca Tettamanti <kronos.it@...il.com> wrote:
>
>> On Fri, Sep 5, 2008 at 10:18 PM, H. Peter Anvin <hpa@...nel.org> wrote:
>> > Peter Zijlstra wrote:
>> >>
>> >> On Fri, 2008-09-05 at 21:17 +0200, Luca Tettamanti wrote:
>> >>>
>> >>> On Thu, Sep 4, 2008 at 10:51 PM, Luca Tettamanti <kronos.it@...il.com>
>> >>> wrote:
>> >>>>
>> >>>> On Thu, Sep 4, 2008 at 4:25 PM, Peter Zijlstra <peterz@...radead.org>
>> >>>> wrote:
>> >>>>>
>> >>>>> Sadly your config just boots, albeit not to userspace due to missing
>> >>>>> drivers.
>> >>>>
>> >>>> Yes, I managed to boot it with qemu... I tried kgdb - without luck -
>> >>>> kernel dies too early.
>> >>>> I also managed to get a stack trace :D
>> >>>>
>> >>>> http://img151.imageshack.us/my.php?image=tracedm1.jpg
>> >>>>
>> >>>> It seems that lockdep is an innocent bystander... the kernel died with
>> >>>> panic() in __reserve_early, and then took another exception while
>> >>>> printing the panic (I guess).
>> >>>> Will add further debug stuff to see wtf is going on.
>> >>>
>> >>> Hum, kernel says:
>> >>>
>> >>> http://img177.imageshack.us/my.php?image=overlappingus2.jpg
>> >>>
>> >>> Overlapping early reservations b98000-eff266 RAMDISK to 200000-d09cf7
>> >>> TEXT DATA BSS
>> >>>
>> >>> It would appear that the initramfs is overlapping the kernel itself,
>> >>> is the boot loader (LILO) doing something stupid?
>> >>
>> >> Suppose it is, lets ask hpa..
>> >>
>> >
>> > It definitely looks like it.
>>
>> Is there anything that the kernel could to do confuse lilo? The issue
>> started appearing with 2.6.27 and the outcome of the boot process
>> varies between versions and seems sensitive to configuration changes
>> (though a "bad" kernel consistently fails).
>
> good question. Does your successful 2.6.26 bootup actually _depend_ on
> the initrd? Or does it perhaps have enough built-in drivers that make it
> boot just fine?

The image is mostly modular (e.g. ahci drivers + LVM + fs are on the
ramdisk), see:
http://marc.info/?l=linux-kernel&m=122046971607455&q=p3

> or perhaps something made your v2.6.27 bzImage larger so that the
> overlap happens - while it didnt before.

The compressed image (bzImage) is roughly the same size as older
kernels (2MB), the uncompressed vmlinux is slightly bigger, but not
much (~100k)

452K    ./mm/built-in.o
100K    ./ipc/built-in.o
8.0K    ./security/built-in.o
3.0M    ./drivers/built-in.o
4.0K    ./usr/built-in.o
216K    ./block/built-in.o
96K     ./init/built-in.o
292K    ./lib/built-in.o
1.3M    ./net/built-in.o
16K     ./crypto/built-in.o
1.1M    ./kernel/built-in.o
1.3M    ./fs/built-in.o
4.0K    ./sound/built-in.o

Luca
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