netdev - Re: [PATCH] net: check for refcount if pop a stacked dst

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Message-ID: <1275648679.2482.43.camel@edumazet-laptop>
Date:	Fri, 04 Jun 2010 12:51:19 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: check for refcount if pop a stacked dst_entry

Le vendredi 04 juin 2010 à 12:41 +0200, Steffen Klassert a écrit :
> xfrm triggers a warning if dst_pop() drops a refcount
> on a noref dst. This patch changes dst_pop() to
> skb_dst_pop(). skb_dst_pop() drops the refcnt only
> on a refcounted dst.
> 
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
>  include/net/dst.h      |    6 +++---
>  net/xfrm/xfrm_output.c |    2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/dst.h b/include/net/dst.h
> index 612069b..acd1538 100644
> --- a/include/net/dst.h
> +++ b/include/net/dst.h
> @@ -250,11 +250,11 @@ static inline void skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev)
>   * Linux networking.  Thus, destinations are stackable.
>   */
>  
> -static inline struct dst_entry *dst_pop(struct dst_entry *dst)
> +static inline struct dst_entry *skb_dst_pop(struct sk_buff *skb)
>  {
> -	struct dst_entry *child = dst_clone(dst->child);
> +	struct dst_entry *child = dst_clone(skb_dst(skb)->child);
>  



> -	dst_release(dst);
> +	skb_dst_drop(skb);
>  	return child;
>  }

Hmm, this might fix the thing, but we probably can do it without the
dst_clone(), if you replace the 

skb_dst_set(skb, dst);

by 

skb_dst_set_noref(skb, dst);

in xfrm_output_one() ?

>  
> diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> index 6a32915..db62a06 100644
> --- a/net/xfrm/xfrm_output.c
> +++ b/net/xfrm/xfrm_output.c
> @@ -95,7 +95,7 @@ resume:
>  			goto error_nolock;
>  		}
>  
> -		dst = dst_pop(dst);
> +		dst = skb_dst_pop(skb);
>  		if (!dst) {
>  			XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR);
>  			err = -EHOSTUNREACH;


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