netdev - [PATCH net-next-2.6 v2] net: build_ehash_secret() and rt_bind

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Message-ID: <1282234245.25476.3.camel@edumazet-laptop>
Date:	Thu, 19 Aug 2010 18:10:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: [PATCH net-next-2.6 v2] net: build_ehash_secret() and
 rt_bind_peer() cleanups

Le jeudi 19 août 2010 à 23:58 +0800, Changli Gao a écrit :

> > -       if (peer)
> > +       peer = cmpxchg(&rt->peer, NULL, peer);
> > +
> > +       if (unlikely(peer))
> 
> It isn't correct, and should be
>      if (unlikely(cmpxchg(&rt->peer, NULL, peer) != NULL))
> 
> >                inet_putpeer(peer);
> >  }
> 
> 

Good catch, thanks !

I was trying to take into account peer being NULL...

[PATCH net-next-2.6] net: build_ehash_secret() and rt_bind_peer() cleanups

Now cmpxchg() is available on all arches, we can use it in
build_ehash_secret() and rt_bind_peer() instead of using spinlocks.

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
---
 net/ipv4/af_inet.c |    8 +++-----
 net/ipv4/route.c   |    9 +--------
 2 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 6a1100c..f581f77 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -227,18 +227,16 @@ EXPORT_SYMBOL(inet_ehash_secret);
 
 /*
  * inet_ehash_secret must be set exactly once
- * Instead of using a dedicated spinlock, we (ab)use inetsw_lock
  */
 void build_ehash_secret(void)
 {
 	u32 rnd;
+
 	do {
 		get_random_bytes(&rnd, sizeof(rnd));
 	} while (rnd == 0);
-	spin_lock_bh(&inetsw_lock);
-	if (!inet_ehash_secret)
-		inet_ehash_secret = rnd;
-	spin_unlock_bh(&inetsw_lock);
+
+	cmpxchg(&inet_ehash_secret, 0, rnd);
 }
 EXPORT_SYMBOL(build_ehash_secret);
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 3f56b6e..85a67c9 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1268,18 +1268,11 @@ skip_hashing:
 
 void rt_bind_peer(struct rtable *rt, int create)
 {
-	static DEFINE_SPINLOCK(rt_peer_lock);
 	struct inet_peer *peer;
 
 	peer = inet_getpeer(rt->rt_dst, create);
 
-	spin_lock_bh(&rt_peer_lock);
-	if (rt->peer == NULL) {
-		rt->peer = peer;
-		peer = NULL;
-	}
-	spin_unlock_bh(&rt_peer_lock);
-	if (peer)
+	if (peer && cmpxchg(&rt->peer, NULL, peer) != NULL)
 		inet_putpeer(peer);
 }
 


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