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Commit 1ca050d9 authored by Oliver Hartkopp's avatar Oliver Hartkopp Committed by David S. Miller
Browse files

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: default avatarOliver Hartkopp <socketcan@hartkopp.net>
Reviewed-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Acked-by: default avatarKurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4c844d97

net/can/af_can.c

+32 −20
Original line number Diff line number Diff line
@@ -85,7 +85,7 @@ static struct kmem_cache *rcv_cache __read_mostly; 


/* 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 */
@@ -115,6 +115,19 @@ static void can_sock_destruct(struct sock *sk) 
	skb_queue_purge(&sk->sk_receive_queue);

}



static struct can_proto *can_try_module_get(int protocol)

{

	struct can_proto *cp;



	rcu_read_lock();

	cp = rcu_dereference(proto_tab[protocol]);

	if (cp && !try_module_get(cp->prot->owner))

		cp = NULL;

	rcu_read_unlock();



	return cp;

}



static int can_create(struct net *net, struct socket *sock, int protocol,

		      int kern)

{
@@ -130,9 +143,12 @@ static int can_create(struct net *net, struct socket *sock, int protocol, 
	if (!net_eq(net, &init_net))

		return -EAFNOSUPPORT;



	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);



		/*
@@ -143,22 +159,18 @@ static int can_create(struct net *net, struct socket *sock, int protocol, 
		if (err && printk_ratelimit())

			printk(KERN_ERR "can: request_module "

			       "(can-proto-%d) failed.\n", protocol);



		cp = can_try_module_get(protocol);

	}

#endif



	spin_lock(&proto_tab_lock);

	cp = proto_tab[protocol];

	if (cp && !try_module_get(cp->prot->owner))

		cp = NULL;

	spin_unlock(&proto_tab_lock);



	/* check for available protocol and correct usage */



	if (!cp)

		return -EPROTONOSUPPORT;



	if (cp->type != sock->type) {

		err = -EPROTONOSUPPORT;

		err = -EPROTOTYPE;

		goto errout;

	}
@@ -694,15 +706,16 @@ int can_proto_register(struct can_proto *cp) 
	if (err < 0)

		return err;



	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 (err < 0)

		proto_unregister(cp->prot);
@@ -719,13 +732,12 @@ 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();



	proto_unregister(cp->prot);

}