Re: [PATCH] net: check for refcount if pop a stacked dst_entry

Eric Dumazet
2010-06-04T10:51:23Z

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@secunet.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;