linux-kernel - Re: kdump fails to load and crashes [was: mmotm 2009-11-01-10-01 uploaded]

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Message-ID: <4AF048D1.4090402@gmail.com>
Date:	Tue, 03 Nov 2009 16:14:25 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org, mm-commits@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, hbabu@...ibm.com,
	kexec@...ts.infradead.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: kdump fails to load and crashes [was: mmotm 2009-11-01-10-01
 uploaded]

On 11/03/2009 03:44 PM, Vivek Goyal wrote:
> On Tue, Nov 03, 2009 at 12:11:58AM +0100, Jiri Slaby wrote:
>> On 11/01/2009 07:07 PM, akpm@...ux-foundation.org wrote:
>>> The mm-of-the-moment snapshot 2009-11-01-10-01 has been uploaded to
>>
>> Hi, kdump loading crashes:
>> BUG: unable to handle kernel paging request at ffff8800010a7000
>> IP: [<ffffffff8101cd8b>] machine_kexec_prepare+0x16b/0x13e0
>> PGD 1806063 PUD 180a063 PMD 10001e1
...
>> ffff8800010a7000 should be OK, as crashkernel=64M@16M was passed to the
>> kernel.
>>
> 
> This is strange. As you said, ffff8800010a7000, should be a valid address
> as you reserved memory from 16M.

Hmm, PMD has not RW bit set and we do store (see below).

> I took above -mm and for me kernel loads fine. I reserved memory 64M@32M
> as by default kernel is loading at address 16M.
> 
> How does your /proc/iomem look like in first kernel?

I'm not any longer on that machine. init_pgtable() overwrites random
memory, so possibly even host's page tables, hence the oops above, I
suppose.

I'm currently chasing it down in the qemu virtual machine, since I
already got a garbage into my ~/.viminfo (some overwritten page got
flushed, I guess).

There /proc/iomem looks like:
00100000-12beffff : System RAM
  01000000-04ffffff : Crash kernel
    01000000-014680c2 : Kernel code
    014680c3-016f39f7 : Kernel data
    0175b000-017d97ab : Kernel bss

I'll keep you informed.
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