From: "Petr Vandrovec" <VANDROVE@vc.cvut.cz>
Organization: CC CTU Prague
To: Andrew Morton <akpm@digeo.com>
Date: Fri, 8 Nov 2002 21:33:24 +0200
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Subject: Re: 2.5.46-bk3: BUG in skbuff.c:178
Cc: linux-kernel@vger.kernel.org, bwindle@fint.org, acme@conectiva.com.br
Message-ID: <6F45EB551A2@vcnet.vc.cvut.cz>
Sender: linux-kernel-owner@vger.kernel.org
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On  8 Nov 02 at 12:01, Andrew Morton wrote:
> > Single-CPU system, running 2.5.46-bk3. Whiling compiling bk4, and running
> > a script that was pinging every host on my subnet (I was running arp -a
> > to see what was in the arp table at the time), I hit this BUG.
> 
> I'd be suspecting the seq_file conversion in arp.c.  The read_lock_bh()
> stuff in there looks, umm, unclear ;)

Yes, see my emails from 23th Oct, 25th Oct (2.5.44: Strange oopses from 
userspace), from Nov 6th + Nov 7th: Preempt count check when leaving
IRQ.

But while yesterday I had no idea, today I have one (it looks like that
nobody else is going to fix it for me :-( ) :
seq subsystem can call arp_seq_start/next/stop several times, but
state->is_pneigh is set to 0 only once, by memset in arp_seq_open :-(

I think that arp_seq_start should do

  {
+   struct arp_iter_state* state = seq->private;
+   seq->is_pneigh = 0;
+   seq->bucket = 0;
    read_lock_bh(&arp_tbl.lock);
    return *pos ? arp_get_bucket(seq, pos) : (void *)1;
  }

and we can drop memset from arp_seq_open. I'll try it, and if it will
survive my tests, I'll send real patch.  
  
                                        Best regards,
                                                Petr Vandrovec
                                                vandrove@vc.cvut.cz
                                                
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