netdev - [PATCH net-next] dst: no need to take reference on DST

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Message-Id: <51b54bc66109594459e1a08c9022c5c48f20d910.1417889528.git.hannes@stressinduktion.org>
Date:	Sat,  6 Dec 2014 19:19:42 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	netdev@...r.kernel.org
Cc:	Eric Dumazet <edumazet@...gle.com>, Julian Anastasov <ja@....bg>
Subject: [PATCH net-next] dst: no need to take reference on DST_NOCACHE dsts

Since commit f8864972126899 ("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@...gle.com>
Cc: Julian Anastasov <ja@....bg>
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
---
 include/linux/skbuff.h          | 23 ++---------------------
 net/core/dst.c                  | 24 ------------------------
 net/netfilter/ipvs/ip_vs_xmit.c |  4 ++--
 3 files changed, 4 insertions(+), 47 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 7691ad5..70ebc79 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -718,9 +718,6 @@ 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
@@ -733,24 +730,8 @@ 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;
 }
 
 /**
diff --git a/net/core/dst.c b/net/core/dst.c
index a028409..e956ce6 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -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
diff --git a/net/netfilter/ipvs/ip_vs_xmit.c b/net/netfilter/ipvs/ip_vs_xmit.c
index 1f93313..3aedbda 100644
--- a/net/netfilter/ipvs/ip_vs_xmit.c
+++ b/net/netfilter/ipvs/ip_vs_xmit.c
@@ -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
-- 
1.9.3

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