netdev - Re: [PANIC] lro + iscsi or lro + skb text search causes panic

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Message-ID: <497EA5B5.5090806@cs.wisc.edu>
Date:	Tue, 27 Jan 2009 00:12:05 -0600
From:	Mike Christie <michaelc@...wisc.edu>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	David Miller <davem@...emloft.net>, jesse.brandeburg@...el.com,
	netdev@...r.kernel.org, olaf.kirch@...cle.com, tgraf@...g.ch,
	kkeil@...e.de
Subject: Re: [PANIC] lro + iscsi or lro + skb text search causes panic

Herbert Xu wrote:
> On Sun, Jan 25, 2009 at 09:32:22PM -0800, David Miller wrote:
>> From: Mike Christie <michaelc@...wisc.edu>
>> Date: Thu, 22 Jan 2009 18:04:11 -0600
>>
>>> With the patch running against linus's git tree, my box locks
>>> up. You cannot ping it. I do not get a oops or anything in the logs,
>>> and the keyboard does not respond. I will try to get some oops
>>> output and more info.
>> Herbert, any idea offhand?
> 
> Yeah, I missed an offset update in there :) Here's a better version.
> 
> net: Fix frag_list handling in skb_seq_read
> 
> The frag_list handling was broken in skb_seq_read:
> 
> 1) We didn't add the stepped offset when looking at the head
> are of fragments other than the first.
> 
> 2) We didn't take the stepped offset away when setting the data
> pointer in the head area.
> 
> 3) The frag index wasn't reset.
> 
> This patch fixes both issues.
> 

It oopsd for me in skb_seq_read. addr2line said it was 
linux-2.6/net/core/skbuff.c:2228, which is this line:


while (st->frag_idx < skb_shinfo(st->cur_skb)->nr_frags) {


I added some printks in there and it looks like we hit this:

         } else if (st->root_skb == st->cur_skb &&
                    skb_shinfo(st->root_skb)->frag_list) {
                 st->cur_skb = skb_shinfo(st->root_skb)->frag_list;
                 st->frag_idx = 0;
                 goto next_skb;
         }


Then when we hit the goto and start again, and we oops when we hit that 
"while (st->frag_idx < skb_shinfo(st->cur_skb)->nr_frags)" line.
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