can: convert protocol handling to RCU

This patch removes spin_locks at CAN socket creation time by using RCU.

Inspired by the discussion with Kurt van Dijck and Eric Dumazet the RCU code
was partly derived from af_phonet.c

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: David S. Miller <davem@davemloft.net>
git-svn-id: svn://svn.berlios.de//socketcan/trunk@1238 030b6a49-0b11-0410-94ab-b0dab22257f2

diff --git a/kernel/2.6/net/can/af_can.c b/kernel/2.6/net/can/af_can.c
index 98b9f36c92c33079a2b3531229d497036b8843e9..81756d15871f6af3397bbb7a036552c2accb5728 100644 (file)
--- a/kernel/2.6/net/can/af_can.c
+++ b/kernel/2.6/net/can/af_can.c
@@ -102,7 +102,7 @@ static kmem_cache_t *rcv_cache;
 
 /* table of registered CAN protocols */
 static struct can_proto *proto_tab[CAN_NPROTO] __read_mostly;
-static DEFINE_SPINLOCK(proto_tab_lock);
+static DEFINE_MUTEX(proto_tab_lock);
 
 struct timer_list can_stattimer;   /* timer for statistics update */
 struct s_stats    can_stats;       /* packet statistics */
@@ -140,6 +140,24 @@ static void can_sock_destruct(struct sock *sk)
 #endif
 }
 
+static struct can_proto *can_try_module_get(int protocol)
+{
+       struct can_proto *cp;
+
+       rcu_read_lock();
+       cp = rcu_dereference(proto_tab[protocol]);
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,12)
+       if (cp && !try_module_get(cp->prot->owner))
+               cp = NULL;
+#else
+       if (cp && !try_module_get(cp->owner))
+               cp = NULL;
+#endif
+       rcu_read_unlock();
+
+       return cp;
+}
+
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,33)
 static int can_create(struct net *net, struct socket *sock, int protocol, int kern)
 #elif LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,24)
@@ -162,9 +180,12 @@ static int can_create(struct socket *sock, int protocol)
                return -EAFNOSUPPORT;
 #endif
 
+       cp = can_try_module_get(protocol);
+
 #ifdef CONFIG_MODULES
-       /* try to load protocol module kernel is modular */
-       if (!proto_tab[protocol]) {
+       if (!cp) {
+               /* try to load protocol module if kernel is modular */
+
                err = request_module("can-proto-%d", protocol);
 
                /*
@@ -175,19 +196,10 @@ static int can_create(struct socket *sock, int protocol)
                if (err && printk_ratelimit())
                        printk(KERN_ERR "can: request_module "
                               "(can-proto-%d) failed.\n", protocol);
-       }
-#endif
 
-       spin_lock(&proto_tab_lock);
-       cp = proto_tab[protocol];
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,12)
-       if (cp && !try_module_get(cp->prot->owner))
-               cp = NULL;
-#else
-       if (cp && !try_module_get(cp->owner))
-               cp = NULL;
+               cp = can_try_module_get(protocol);
+       }
 #endif
-       spin_unlock(&proto_tab_lock);
 
        /* check for available protocol and correct usage */
 
@@ -195,7 +207,7 @@ static int can_create(struct socket *sock, int protocol)
                return -EPROTONOSUPPORT;
 
        if (cp->type != sock->type) {
-               err = -EPROTONOSUPPORT;
+               err = -EPROTOTYPE;
                goto errout;
        }
 
@@ -863,15 +875,16 @@ int can_proto_register(struct can_proto *cp)
                return err;
 #endif
 
-       spin_lock(&proto_tab_lock);
+       mutex_lock(&proto_tab_lock);
+
        if (proto_tab[proto]) {
                printk(KERN_ERR "can: protocol %d already registered\n",
                       proto);
                err = -EBUSY;
        } else
-               proto_tab[proto] = cp;
+               rcu_assign_pointer(proto_tab[proto], cp);
 
-       spin_unlock(&proto_tab_lock);
+       mutex_unlock(&proto_tab_lock);
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,12)
        if (err < 0)
@@ -890,13 +903,12 @@ void can_proto_unregister(struct can_proto *cp)
 {
        int proto = cp->protocol;
 
-       spin_lock(&proto_tab_lock);
-       if (!proto_tab[proto]) {
-               printk(KERN_ERR "BUG: can: protocol %d is not registered\n",
-                      proto);
-       }
-       proto_tab[proto] = NULL;
-       spin_unlock(&proto_tab_lock);
+       mutex_lock(&proto_tab_lock);
+       BUG_ON(proto_tab[proto] != cp);
+       rcu_assign_pointer(proto_tab[proto], NULL);
+       mutex_unlock(&proto_tab_lock);
+
+       synchronize_rcu();
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,12)
        proto_unregister(cp->prot);