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, 5 insertions, 26 deletions

diff --git a/net/ipv4/protocol.c b/net/ipv4/protocol.c
index f2d297351405..65699c24411c 100644
--- a/net/ipv4/protocol.c
+++ b/net/ipv4/protocol.c
@@ -28,8 +28,7 @@
 #include <linux/spinlock.h>
 #include <net/protocol.h>
 
-const struct net_protocol *inet_protos[MAX_INET_PROTOS] ____cacheline_aligned_in_smp;
-static DEFINE_SPINLOCK(inet_proto_lock);
+const struct net_protocol *inet_protos[MAX_INET_PROTOS] __read_mostly;
 
 /*
  *      Add a protocol handler to the hash tables
@@ -37,20 +36,9 @@ static DEFINE_SPINLOCK(inet_proto_lock);
 
 int inet_add_protocol(const struct net_protocol *prot, unsigned char protocol)
 {
-        int hash, ret;
+        int hash = protocol & (MAX_INET_PROTOS - 1);
 
-        hash = protocol & (MAX_INET_PROTOS - 1);
-
-        spin_lock_bh(&inet_proto_lock);
-        if (inet_protos[hash]) {
-                ret = -1;
-        } else {
-                inet_protos[hash] = prot;
-                ret = 0;
-        }
-        spin_unlock_bh(&inet_proto_lock);
-
-        return ret;
+        return !cmpxchg(&inet_protos[hash], NULL, prot) ? 0 : -1;
 }
 EXPORT_SYMBOL(inet_add_protocol);
 
@@ -60,18 +48,9 @@ EXPORT_SYMBOL(inet_add_protocol);
 
 int inet_del_protocol(const struct net_protocol *prot, unsigned char protocol)
 {
-        int hash, ret;
-
-        hash = protocol & (MAX_INET_PROTOS - 1);
+        int ret, hash = protocol & (MAX_INET_PROTOS - 1);
 
-        spin_lock_bh(&inet_proto_lock);
-        if (inet_protos[hash] == prot) {
-                inet_protos[hash] = NULL;
-                ret = 0;
-        } else {
-                ret = -1;
-        }
-        spin_unlock_bh(&inet_proto_lock);
+        ret = (cmpxchg(&inet_protos[hash], prot, NULL) == prot) ? 0 : -1;
 
         synchronize_net();