Commit dbfc4fb7 authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by David S. Miller
Browse files

dst: no need to take reference on DST_NOCACHE dsts 



Since commit f8864972 ("ipv4: fix dst race in sk_dst_get()")
DST_NOCACHE dst_entries get freed by RCU. So there is no need to get a
reference on them when we are in rcu protected sections.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Reviewed-by: default avatarJulian Anastasov <ja@ssi.bg>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c19be735

include/linux/skbuff.h

+2 −21
Original line number Diff line number Diff line
@@ -717,9 +717,6 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst) 
	skb->_skb_refdst = (unsigned long)dst;

}



void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst,

			 bool force);



/**

 * skb_dst_set_noref - sets skb dst, hopefully, without taking reference

 * @skb: buffer
@@ -732,24 +729,8 @@ void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst, 
 */

static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)

{

	__skb_dst_set_noref(skb, dst, false);

}



/**

 * skb_dst_set_noref_force - sets skb dst, without taking reference

 * @skb: buffer

 * @dst: dst entry

 *

 * Sets skb dst, assuming a reference was not taken on dst.

 * No reference is taken and no dst_release will be called. While for

 * cached dsts deferred reclaim is a basic feature, for entries that are

 * not cached it is caller's job to guarantee that last dst_release for

 * provided dst happens when nobody uses it, eg. after a RCU grace period.

 */

static inline void skb_dst_set_noref_force(struct sk_buff *skb,

					   struct dst_entry *dst)

{

	__skb_dst_set_noref(skb, dst, true);

	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());

	skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;

}



/**

net/core/dst.c

+0 −24
Original line number Diff line number Diff line
@@ -327,30 +327,6 @@ void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old) 
}

EXPORT_SYMBOL(__dst_destroy_metrics_generic);



/**

 * __skb_dst_set_noref - sets skb dst, without a reference

 * @skb: buffer

 * @dst: dst entry

 * @force: if force is set, use noref version even for DST_NOCACHE entries

 *

 * Sets skb dst, assuming a reference was not taken on dst

 * skb_dst_drop() should not dst_release() this dst

 */

void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst, bool force)

{

	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());

	/* If dst not in cache, we must take a reference, because

	 * dst_release() will destroy dst as soon as its refcount becomes zero

	 */

	if (unlikely((dst->flags & DST_NOCACHE) && !force)) {

		dst_hold(dst);

		skb_dst_set(skb, dst);

	} else {

		skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;

	}

}

EXPORT_SYMBOL(__skb_dst_set_noref);



/* Dirty hack. We did it in 2.2 (in __dst_free),

 * we have _very_ good reasons not to repeat

 * this mistake in 2.3, but we have no choice

net/netfilter/ipvs/ip_vs_xmit.c

+2 −2
Original line number Diff line number Diff line
@@ -343,7 +343,7 @@ __ip_vs_get_out_rt(int skb_af, struct sk_buff *skb, struct ip_vs_dest *dest, 
	skb_dst_drop(skb);

	if (noref) {

		if (!local)

			skb_dst_set_noref_force(skb, &rt->dst);

			skb_dst_set_noref(skb, &rt->dst);

		else

			skb_dst_set(skb, dst_clone(&rt->dst));

	} else
@@ -487,7 +487,7 @@ __ip_vs_get_out_rt_v6(int skb_af, struct sk_buff *skb, struct ip_vs_dest *dest, 
	skb_dst_drop(skb);

	if (noref) {

		if (!local)

			skb_dst_set_noref_force(skb, &rt->dst);

			skb_dst_set_noref(skb, &rt->dst);

		else

			skb_dst_set(skb, dst_clone(&rt->dst));

	} else

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