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

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Date:	Thu, 16 Dec 2010 14:58:14 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
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 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?

	Yinghai
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