net: inet_add_protocol() can use cmpxchg()

Use cmpxchg() to get rid of spinlocks in inet_add_protocol() and
friends.

inet_protos[] & inet6_protos[] are moved to read_mostly section

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 28 deletions

diff --git a/net/ipv6/protocol.c b/net/ipv6/protocol.c
index 1fa3468f0f32..9bb936ae2452 100644
--- a/net/ipv6/protocol.c
+++ b/net/ipv6/protocol.c
@@ -25,28 +25,14 @@
 #include <linux/spinlock.h>
 #include <net/protocol.h>
 
-const struct inet6_protocol *inet6_protos[MAX_INET_PROTOS];
-static DEFINE_SPINLOCK(inet6_proto_lock);
-
+const struct inet6_protocol *inet6_protos[MAX_INET_PROTOS] __read_mostly;
 
 int inet6_add_protocol(const struct inet6_protocol *prot, unsigned char protocol)
 {
-        int ret, hash = protocol & (MAX_INET_PROTOS - 1);
-
-        spin_lock_bh(&inet6_proto_lock);
-
-        if (inet6_protos[hash]) {
-                ret = -1;
-        } else {
-                inet6_protos[hash] = prot;
-                ret = 0;
-        }
-
-        spin_unlock_bh(&inet6_proto_lock);
+        int hash = protocol & (MAX_INET_PROTOS - 1);
 
-        return ret;
+        return !cmpxchg(&inet6_protos[hash], NULL, prot) ? 0 : -1;
 }
-
 EXPORT_SYMBOL(inet6_add_protocol);
 
 /*
@@ -57,20 +43,10 @@ int inet6_del_protocol(const struct inet6_protocol *prot, unsigned char protocol
 {
         int ret, hash = protocol & (MAX_INET_PROTOS - 1);
 
-        spin_lock_bh(&inet6_proto_lock);
-
-        if (inet6_protos[hash] != prot) {
-                ret = -1;
-        } else {
-                inet6_protos[hash] = NULL;
-                ret = 0;
-        }
-
-        spin_unlock_bh(&inet6_proto_lock);
+        ret = (cmpxchg(&inet6_protos[hash], prot, NULL) == prot) ? 0 : -1;
 
         synchronize_net();
 
         return ret;
 }
-
 EXPORT_SYMBOL(inet6_del_protocol);