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Re: kernel bug using 2.6.23-rc9

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: kernel bug using 2.6.23-rc9
From: David Daney <ddaney@avtrex.com>
Date: Fri, 05 Oct 2007 08:57:24 -0700
Cc: Giuseppe Sacco <giuseppe@eppesuigoccas.homedns.org>, linux-mips@linux-mips.org
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Ralf Baechle wrote:
On Thu, Oct 04, 2007 at 02:49:13PM +0200, Giuseppe Sacco wrote:

Hi, while testing the latest kernel on SGI O2 I got may kernel bugs like
this:

Kernel bug detected[#9]:
Cpu 0
$ 0   : 0000000000000000 ffffffff9001fce0 0000000000000001 0000000000000f18
$ 4   : 980000000111b4b8 000000007f955f18 ffffffff80400000 0000000000003fff
$ 8   : 00000000000050f1 000000007f955f18 9800000006073d68 9800000006073d60
$12   : 0000000000000010 ffffffff80000008 ffffffff80091680 0000000000000000
$16   : 980000000111b4b8 980000000768ddd0 000000000000000e 000000007f955f18
$20   : 9800000000581908 9800000007898080 9800000006073d68 9800000006073d60
$24 : 0000000000478284 000000002ac30580 $28 : 9800000006070000 9800000006073cd0 0000000000000000 ffffffff8001b390
Hi    : 000000000000f2d3
Lo    : 00000000000050f1
epc   : ffffffff8001c800 kmap_coherent+0x10/0x118     Tainted: G      D
ra    : ffffffff8001b390 __flush_anon_page+0x70/0x90

Very interesting.  Can you describe me your setup or maybe even come up
with a test case for this?

Perhaps: 'cat /proc/self/cmdline'

As we were hacking O_DIRECT support into 2.6.15, I found what seems like a very similar situation.

It seems that all users of get_user_pages() *except* /proc/*/[cmdline|environ] call get_user_pages() with addresses aligned on page boundaries. I am not sure if that is the problem here, but it seems similar.

David Daney.

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