linux-kernel - Re: [Bug #12409] NULL pointer dereference at get

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Date:	Sat, 7 Feb 2009 11:34:00 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	frederik.deweerdt@...og.eu, rjw@...k.pl
Cc:	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org
Subject: Re: [Bug #12409] NULL pointer dereference at get_stats()

Hello.

On Mon, Jan 19, 2009 at 10:45:43PM +0100, Rafael J. Wysocki wrote:
> This message has been generated automatically as a part of a report
> of regressions introduced between 2.6.27 and 2.6.28.
> 
> The following bug entry is on the current list of known regressions
> introduced between 2.6.27 and 2.6.28.  Please verify if it still should
> be listed and let me know (either way).
> 
> 
> Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=12409
> Subject		: NULL pointer dereference at get_stats()
> Submitter	: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> Date		: 2008-12-30 12:53 (21 days old)
> References	: http://marc.info/?l=linux-kernel&m=123064167008695&w=4
> Handled-By	: Frederik Deweerdt <frederik.deweerdt@...og.eu>

This bug happens when "nolapic" option is given.
This bug exists in 2.6.27.15 and 2.6.28.4 .
This bug does not exist in 2.6.26.8 and 2.6.29-rc3-git10 .

How to reproduce:
(1) Prepare x86 machine with 2 cpus.
(2) Add "nolapic" and "init=/bin/sh" options at the kernel command line.
(3) Do "cat /sys/class/net/lo/statistics/rx_packets".

If you apply a patch at http://lkml.org/lkml/2009/1/5/557 , you will notice
"lb_stats == NULL for CPU 1" message.
I think "nolapic" option causes for_each_possible_cpu() to reach CPU 1
by some error.

Frederik Deweerdt wrote:
> Hello Rafael,
> 
> Not sure what the status should be for that one, it sure seems vmware
> related, and I don't have one handy.
> 
> Regards,
> Frederik

I think this bug will happen in native environment too.
http://lkml.org/lkml/2009/1/4/349
But due to driver initialization failure caused by "nolapic" option,
I can't reach /sbin/init on native ThinkPad X60 environment.

Regards.
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