o net: improve the current module infrastructure

As per discussions in netdev we'll probably be moving to a brand new scheme, but this
set of changesets have been discussed and are an improvement to the current situation
and were already done prior to this thread happening.

include/linux/net.h

@@ -89,9 +89,11 @@ struct page;
 struct kiocb;
 struct sockaddr;
 struct msghdr;
+struct module;
 
 struct proto_ops {
 	int		family;
+	struct module	*owner;
 	int		(*release)   (struct socket *sock);
 	int		(*bind)	     (struct socket *sock,
 				      struct sockaddr *umyaddr,
@@ -127,8 +129,6 @@ struct proto_ops {
 				      int offset, size_t size, int flags);
 };
 
-struct module;
-
 struct net_proto_family {
 	int		family;
 	int		(*create)(struct socket *sock, int protocol);
@@ -140,9 +140,6 @@ struct net_proto_family {
 	struct module	*owner;
 };
 
-extern int	     net_family_get(int family);
-extern void	     net_family_put(int family);
-
 struct iovec;
 
 extern int	     sock_wake_async(struct socket *sk, int how, int band);
@@ -227,7 +224,7 @@ SOCKCALL_WRAP(name, mmap, (struct file *file, struct socket *sock, struct vm_are
 	      \
 static struct proto_ops name##_ops = {			\
 	.family		= fam,				\
-							\
+	.owner		= THIS_MODULE,			\
 	.release	= __lock_##name##_release,	\
 	.bind		= __lock_##name##_bind,		\
 	.connect	= __lock_##name##_connect,	\

include/net/sock.h

@@ -43,7 +43,7 @@
 #include <linux/config.h>
 #include <linux/timer.h>
 #include <linux/cache.h>
-
+#include <linux/module.h>
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>	/* struct sk_buff */
 #include <linux/security.h>
@@ -197,6 +197,7 @@ struct sock {
 	void			*user_data;
   
 	/* Callbacks */
+	struct module		*owner;
 	void			(*state_change)(struct sock *sk);
 	void			(*data_ready)(struct sock *sk,int bytes);
 	void			(*write_space)(struct sock *sk);
@@ -270,6 +271,23 @@ struct proto {
 	} stats[NR_CPUS];
 };
 
+static __inline__ void sk_set_owner(struct sock *sk, struct module *owner)
+{
+	/*
+	 * One should use sk_set_owner just once, after struct sock creation,
+	 * be it shortly after sk_alloc or after a function that returns a new
+	 * struct sock (and that down the call chain called sk_alloc), e.g. the
+	 * IPv4 and IPv6 modules share tcp_create_openreq_child, so if
+	 * tcp_create_openreq_child called sk_set_owner IPv6 would have to
+	 * change the ownership of this struct sock, with one not needed
+	 * transient sk_set_owner call.
+	 */
+	if (unlikely(sk->owner != NULL))
+		BUG();
+	sk->owner = owner;
+	__module_get(owner);
+}
+
 /* Called with local bh disabled */
 static __inline__ void sock_prot_inc_use(struct proto *prot)
 {

net/core/sock.c

@@ -591,8 +591,6 @@ struct sock *sk_alloc(int family, int priority, int zero_it, kmem_cache_t *slab)
 {
 	struct sock *sk = NULL;
 
-	if (!net_family_get(family))
-		goto out;
 	if (!slab)
 		slab = sk_cachep;
 	sk = kmem_cache_alloc(slab, priority);
@@ -604,16 +602,14 @@ struct sock *sk_alloc(int family, int priority, int zero_it, kmem_cache_t *slab)
 			sock_lock_init(sk);
 		}
 		sk->slab = slab;
-	} else
-		net_family_put(family);
-out:
+	}
 	return sk;
 }
 
 void sk_free(struct sock *sk)
 {
 	struct sk_filter *filter;
-	const int family = sk->family;
+	struct module *owner = sk->owner;
 
 	if (sk->destruct)
 		sk->destruct(sk);
@@ -628,7 +624,7 @@ void sk_free(struct sock *sk)
 		printk(KERN_DEBUG "sk_free: optmem leakage (%d bytes) detected.\n", atomic_read(&sk->omem_alloc));
 
 	kmem_cache_free(sk->slab, sk);
-	net_family_put(family);
+	module_put(owner);
 }
 
 void __init sk_init(void)
@@ -1112,6 +1108,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 	sk->rcvlowat		=	1;
 	sk->rcvtimeo		=	MAX_SCHEDULE_TIMEOUT;
 	sk->sndtimeo		=	MAX_SCHEDULE_TIMEOUT;
+	sk->owner		=	NULL;
 
 	atomic_set(&sk->refcnt, 1);
 }

net/socket.c

@@ -141,36 +141,6 @@ static struct file_operations socket_file_ops = {
 
 static struct net_proto_family *net_families[NPROTO];
 
-static __inline__ void net_family_bug(int family)
-{
-	printk(KERN_ERR "%d is not yet sock_registered!\n", family);
-	BUG();
-}
-
-int net_family_get(int family)
-{
-	struct net_proto_family *prot = net_families[family];
-	int rc = 1;
-
-	barrier();
-	if (likely(prot != NULL))
-		rc = try_module_get(prot->owner);
-	else
-		net_family_bug(family);
-	return rc;
-}
-
-void net_family_put(int family)
-{
-	struct net_proto_family *prot = net_families[family];
-
-	barrier();
-	if (likely(prot != NULL))
-		module_put(prot->owner);
-	else
-		net_family_bug(family);
-}
-
 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
 static atomic_t net_family_lockct = ATOMIC_INIT(0);
 static spinlock_t net_family_lock = SPIN_LOCK_UNLOCKED;
@@ -535,11 +505,11 @@ struct file_operations bad_sock_fops = {
 void sock_release(struct socket *sock)
 {
 	if (sock->ops) {
-		const int family = sock->ops->family;
+		struct module *owner = sock->ops->owner;
 
 		sock->ops->release(sock);
 		sock->ops = NULL;
-		net_family_put(family);
+		module_put(owner);
 	}
 
 	if (sock->fasync_list)
@@ -1091,19 +1061,37 @@ int sock_create(int family, int type, int protocol, struct socket **res)
 
 	sock->type  = type;
 
+	/*
+	 * We will call the ->create function, that possibly is in a loadable
+	 * module, so we have to bump that loadable module refcnt first.
+	 */
 	i = -EAFNOSUPPORT;
-	if (!net_family_get(family))
+	if (!try_module_get(net_families[family]->owner))
 		goto out_release;
 
 	if ((i = net_families[family]->create(sock, protocol)) < 0)
-		goto out_release;
-
+		goto out_module_put;
+	/*
+	 * Now to bump the refcnt of the [loadable] module that owns this
+	 * socket at sock_release time we decrement its refcnt.
+	 */
+	if (!try_module_get(sock->ops->owner)) {
+		sock->ops = NULL;
+		goto out_module_put;
+	}
+	/*
+	 * Now that we're done with the ->create function, the [loadable]
+	 * module can have its refcnt decremented
+	 */
+	module_put(net_families[family]->owner);
 	*res = sock;
 	security_socket_post_create(sock, family, type, protocol);
 
 out:
 	net_family_read_unlock();
 	return i;
+out_module_put:
+	module_put(net_families[family]->owner);
 out_release:
 	sock_release(sock);
 	goto out;
@@ -1288,28 +1276,30 @@ asmlinkage long sys_accept(int fd, struct sockaddr *upeer_sockaddr, int *upeer_a
 	if (err)
 		goto out_release;
 
-	err = -EAFNOSUPPORT;
-	if (!net_family_get(sock->ops->family))
-		goto out_release;
+	/*
+	 * We don't need try_module_get here, as the listening socket (sock)
+	 * has the protocol module (sock->ops->owner) held.
+	 */
+	__module_get(sock->ops->owner);
 
 	err = sock->ops->accept(sock, newsock, sock->file->f_flags);
 	if (err < 0)
-		goto out_family_put;
+		goto out_module_put;
 
 	if (upeer_sockaddr) {
 		if(newsock->ops->getname(newsock, (struct sockaddr *)address, &len, 2)<0) {
 			err = -ECONNABORTED;
-			goto out_family_put;
+			goto out_module_put;
 		}
 		err = move_addr_to_user(address, len, upeer_sockaddr, upeer_addrlen);
 		if (err < 0)
-			goto out_family_put;
+			goto out_module_put;
 	}
 
 	/* File flags are not inherited via accept() unlike another OSes. */
 
 	if ((err = sock_map_fd(newsock)) < 0)
-		goto out_family_put;
+		goto out_module_put;
 
 	security_socket_post_accept(sock, newsock);
 
@@ -1317,8 +1307,8 @@ asmlinkage long sys_accept(int fd, struct sockaddr *upeer_sockaddr, int *upeer_a
 	sockfd_put(sock);
 out:
 	return err;
-out_family_put:
-	net_family_put(sock->ops->family);
+out_module_put:
+	module_put(sock->ops->owner);
 out_release:
 	sock_release(newsock);
 	goto out_put;