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Date:	Mon, 25 Feb 2008 12:42:20 +0100
From:	"Jann Traschewski" <jann@....de>
To:	"'Jarek Poplawski'" <jarkao2@...il.com>
Cc:	<netdev@...r.kernel.org>, "'Ralf Baechle'" <ralf@...ux-mips.org>
Subject: Re: [BUG][AX25] spinlock lockup

Applied. Thanks!
Regards,
Jann

> -----Urspr√ľngliche Nachricht-----
> Von: Jarek Poplawski [mailto:jarkao2@...il.com] 
> Gesendet: Sonntag, 24. Februar 2008 20:51
> An: Jann Traschewski
> Cc: netdev@...r.kernel.org; 'Ralf Baechle'
> Betreff: Re: [BUG][AX25] spinlock lockup
> 
> On Sun, Feb 24, 2008 at 04:10:29AM +0100, Jann Traschewski wrote:
> > Hello,
> 
> Hi!
> 
> > I got a "spinlock lockup" using the latest Kernel 2.6.24.2 
> with recent 
> > patches from Jarek Poplawski applied.
> ...
> >  ppp_deflate nf_nat zlib_deflateBUG: unable to handle kernel NULL 
> > pointer dereference zlib_inflate nf_conntrack_ipv4 bsd_comp slhc 
> > ppp_async xt_state
> ...
> > EIP is at skb_append+0x1b/0x30
> ...
> > 00000010 BUG: spinlock lockup on CPU#1, bcm/12213, f40846b8
> 
> Looks like 2 in 1: NULL pointer dereference and (later?) lockup.
> 
> There is only one function in AX25 calling skb_append(), and 
> it really looks suspicious: appends skb after previously 
> enqueued one, but in the meantime this previous skb could be 
> removed from the queue.
> 
> Here is a patch for testing: it fixes this simple way, so 
> this is not fully compatible with the current method, but 
> let's check if this could be a problem?
> 
> Regards,
> Jarek P.
> 
> (testing patch #1)
> 
> ---
> 
>  net/ax25/ax25_subr.c |   11 +++--------
>  1 files changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/net/ax25/ax25_subr.c b/net/ax25/ax25_subr.c 
> index d8f2157..034aa10 100644
> --- a/net/ax25/ax25_subr.c
> +++ b/net/ax25/ax25_subr.c
> @@ -64,20 +64,15 @@ void ax25_frames_acked(ax25_cb *ax25, 
> unsigned short nr)
>  
>  void ax25_requeue_frames(ax25_cb *ax25)  {
> -	struct sk_buff *skb, *skb_prev = NULL;
> +	struct sk_buff *skb;
>  
>  	/*
>  	 * Requeue all the un-ack-ed frames on the output queue 
> to be picked
>  	 * up by ax25_kick called from the timer. This 
> arrangement handles the
>  	 * possibility of an empty output queue.
>  	 */
> -	while ((skb = skb_dequeue(&ax25->ack_queue)) != NULL) {
> -		if (skb_prev == NULL)
> -			skb_queue_head(&ax25->write_queue, skb);
> -		else
> -			skb_append(skb_prev, skb, &ax25->write_queue);
> -		skb_prev = skb;
> -	}
> +	while ((skb = skb_dequeue_tail(&ax25->ack_queue)) != NULL)
> +		skb_queue_head(&ax25->write_queue, skb);
>  }
>  
>  /*

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