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Message-ID: <4D9B58EC.9090903@hartkopp.net>
Date: Tue, 05 Apr 2011 20:01:16 +0200
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: David Miller <davem@...emloft.net>
CC: Linux Netdev List <netdev@...r.kernel.org>,
Kurt Van Dijck <kurt.van.dijck@....be>,
Eric Dumazet <eric.dumazet@...il.com>,
Urs Thuermann <urs@...ogud.escape.de>
Subject: [PATCH net-next-2.6 v2] 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@...tkopp.net>
Reviewed-by: Eric Dumazet <eric.dumazet@...il.com>
---
diff --git a/net/can/af_can.c b/net/can/af_can.c
index 733d66f..a8dcaa4 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -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);
}
--
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