linux-kernel - Re: kdump broken on 2.6.37-rc4

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Date:	Fri, 17 Dec 2010 11:15:05 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maxim Uvarov <muvarov@...il.com>, linux-kernel@...r.kernel.org,
	Neil Horman <nhorman@...hat.com>
Subject: Re: kdump broken on 2.6.37-rc4

On Thu, Dec 16, 2010 at 02:58:14PM -0800, Yinghai Lu wrote:
> On 12/16/2010 02:01 PM, Vivek Goyal wrote:
> > On Thu, Dec 16, 2010 at 09:28:49AM -0800, Yinghai Lu wrote:
> >> On 12/16/2010 08:28 AM, H. Peter Anvin wrote:
> >>> On 12/16/2010 06:39 AM, Vivek Goyal wrote:
> >>>> On Wed, Dec 15, 2010 at 08:29:01PM -0800, Yinghai Lu wrote:
> >>>>> please check
> >>>>>
> >>>>> [PATCH] x86, crashkernel, 32bit: only try to get range under 512M
> >>>>>
> >>>>> Steanishlaw report kdump is 32bit is broken.
> >>>>>
> >>>>> in misc.c for decompresser, it will do sanity checking to make sure heap
> >>>>> heap under 512M.
> >>>>
> >>>> Thanks Yinghai. I am wondering why on 32bit heap has to be with-in 512MB.
> >>>> I think you are referring to following check in
> >>>> arch/x86/boot/compressed/misc.c.
> >>>>
> >>>> 	if (end > ((-__PAGE_OFFSET-(512 <<20)-1) & 0x7fffffff))
> >>>> 		error("Destination address too large");
> >>>>
> >>>> It was introduced here.
> >>>>
> >>>> commit 968de4f02621db35b8ae5239c8cfc6664fb872d8
> >>>> Author: Eric W. Biederman <ebiederm@...ssion.com>
> >>>> Date:   Thu Dec 7 02:14:04 2006 +0100
> >>>>
> >>>>     [PATCH] i386: Relocatable kernel support
> >>>>
> >>>> Eric,
> >>>>
> >>>> It has been long. By any chance would you remember where does above
> >>>> constraint come from?
> >>>>
> >>>
> >>> It might, in fact, be bogus; specifically a proxy for the fact that we
> >>> need the kernel memory including bss and brk below the lowmem boundary,
> >>> which isn't well-defined.
> >>
> >> the brk is complaining if i change that to 
> >>
> >>  	if (end > ((-__PAGE_OFFSET-(128 <<20)-1) & 0x7fffffff))
> >>  		error("Destination address too large");
> >>
> > 
> > Yinghai, 
> > 
> > On my system above change works fine and I can boot into second kernel. So
> > it will boil down to knowing what are the exact constraints on heap for
> > decompression and for 32bit can we allow heap upto 896MB or not.
> 
> really? what is you CONFIG_PAGE_OFFSET? 0x40000000 or 0xc0000000?
> 

I am using CONFIG_PAGE_OFFSET=0xC0000000

Thanks
Vivek
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