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>
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@ -85,7 +85,7 @@ static struct kmem_cache *rcv_cache __read_mostly;
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/* table of registered CAN protocols */
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static struct can_proto *proto_tab[CAN_NPROTO] __read_mostly;
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static DEFINE_SPINLOCK(proto_tab_lock);
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static DEFINE_MUTEX(proto_tab_lock);
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struct timer_list can_stattimer; /* timer for statistics update */
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struct s_stats can_stats; /* packet statistics */
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@ -115,6 +115,19 @@ static void can_sock_destruct(struct sock *sk)
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skb_queue_purge(&sk->sk_receive_queue);
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}
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static struct can_proto *can_try_module_get(int protocol)
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{
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struct can_proto *cp;
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rcu_read_lock();
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cp = rcu_dereference(proto_tab[protocol]);
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if (cp && !try_module_get(cp->prot->owner))
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cp = NULL;
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rcu_read_unlock();
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return cp;
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}
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static int can_create(struct net *net, struct socket *sock, int protocol,
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int kern)
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{
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@ -130,9 +143,12 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
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if (!net_eq(net, &init_net))
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return -EAFNOSUPPORT;
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cp = can_try_module_get(protocol);
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#ifdef CONFIG_MODULES
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/* try to load protocol module kernel is modular */
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if (!proto_tab[protocol]) {
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if (!cp) {
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/* try to load protocol module if kernel is modular */
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err = request_module("can-proto-%d", protocol);
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/*
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@ -143,22 +159,18 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
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if (err && printk_ratelimit())
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printk(KERN_ERR "can: request_module "
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"(can-proto-%d) failed.\n", protocol);
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cp = can_try_module_get(protocol);
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}
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#endif
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spin_lock(&proto_tab_lock);
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cp = proto_tab[protocol];
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if (cp && !try_module_get(cp->prot->owner))
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cp = NULL;
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spin_unlock(&proto_tab_lock);
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/* check for available protocol and correct usage */
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if (!cp)
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return -EPROTONOSUPPORT;
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if (cp->type != sock->type) {
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err = -EPROTONOSUPPORT;
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err = -EPROTOTYPE;
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goto errout;
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}
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@ -694,15 +706,16 @@ int can_proto_register(struct can_proto *cp)
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if (err < 0)
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return err;
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spin_lock(&proto_tab_lock);
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mutex_lock(&proto_tab_lock);
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if (proto_tab[proto]) {
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printk(KERN_ERR "can: protocol %d already registered\n",
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proto);
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err = -EBUSY;
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} else
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proto_tab[proto] = cp;
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rcu_assign_pointer(proto_tab[proto], cp);
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spin_unlock(&proto_tab_lock);
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mutex_unlock(&proto_tab_lock);
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if (err < 0)
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proto_unregister(cp->prot);
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@ -719,13 +732,12 @@ void can_proto_unregister(struct can_proto *cp)
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{
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int proto = cp->protocol;
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spin_lock(&proto_tab_lock);
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if (!proto_tab[proto]) {
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printk(KERN_ERR "BUG: can: protocol %d is not registered\n",
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proto);
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}
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proto_tab[proto] = NULL;
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spin_unlock(&proto_tab_lock);
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mutex_lock(&proto_tab_lock);
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BUG_ON(proto_tab[proto] != cp);
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rcu_assign_pointer(proto_tab[proto], NULL);
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mutex_unlock(&proto_tab_lock);
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synchronize_rcu();
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proto_unregister(cp->prot);
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}
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