netdev - Re: kernel newbie question on kernel panic

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Date:	Mon, 21 Jul 2008 18:07:25 +0200
From:	Daniel Lezcano <dlezcano@...ibm.com>
To:	Filka Michal <Michal.Filka@...ronicsts.com>
CC:	netdev@...r.kernel.org
Subject: Re: kernel newbie question on kernel panic

Filka Michal wrote:
> Hi all,
> 
> I try to create my first kernel module.
> I have following problem. I have a function rp ... interesting part
> follows (just some initialization is ommited - nothing special - the
> function is just a skeleton)
> 
> int rp( struct sk_buff ** skb)
> {
> 	_filter_rule * rule = NULL;
> 
> ...
> 
> 	rule = placebo();
> -->	if( rule == NULL)
> 		printk( KERN_DEBUG "null rule\n");
> 	return 1;
> }
> 
> The rp is called (subsequently) in netfilter (prerouting) hook context,
> so as far as I know it runs in a SoftIRQ.
> 
> The placebo function does nothing - just returns NULL. The problem is in
> line selected (-->).Everything goes until I try to somehow access
> returned value. The access raises kernel panic, seems that some page
> fault happent. If I comment out the line bellow selected (the test), no
> kernel panic happens.
> 
> Questions are:
> - why the page fault happens (some trouble in memory usage, or so?)
> - how to avoid it?
> 
> Thanks for any help
> Michal Filka

What is the definition of _filter_rule ?
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