[NET]: socket family using RCU
Replace the gross custom locking done in socket code for net_family[]
with simple RCU usage. Some reordering necessary to avoid sleep issues
with sock_alloc.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/socket.c b/net/socket.c
index 156f2ef..b5a3fcb 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -59,11 +59,11 @@
*/
#include <linux/mm.h>
-#include <linux/smp_lock.h>
#include <linux/socket.h>
#include <linux/file.h>
#include <linux/net.h>
#include <linux/interrupt.h>
+#include <linux/rcupdate.h>
#include <linux/netdevice.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
@@ -146,51 +146,8 @@
* The protocol list. Each protocol is registered in here.
*/
-static struct net_proto_family *net_families[NPROTO];
-
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
-static atomic_t net_family_lockct = ATOMIC_INIT(0);
static DEFINE_SPINLOCK(net_family_lock);
-
-/* The strategy is: modifications net_family vector are short, do not
- sleep and veeery rare, but read access should be free of any exclusive
- locks.
- */
-
-static void net_family_write_lock(void)
-{
- spin_lock(&net_family_lock);
- while (atomic_read(&net_family_lockct) != 0) {
- spin_unlock(&net_family_lock);
-
- yield();
-
- spin_lock(&net_family_lock);
- }
-}
-
-static __inline__ void net_family_write_unlock(void)
-{
- spin_unlock(&net_family_lock);
-}
-
-static __inline__ void net_family_read_lock(void)
-{
- atomic_inc(&net_family_lockct);
- spin_unlock_wait(&net_family_lock);
-}
-
-static __inline__ void net_family_read_unlock(void)
-{
- atomic_dec(&net_family_lockct);
-}
-
-#else
-#define net_family_write_lock() do { } while(0)
-#define net_family_write_unlock() do { } while(0)
-#define net_family_read_lock() do { } while(0)
-#define net_family_read_unlock() do { } while(0)
-#endif
+static const struct net_proto_family *net_families[NPROTO];
/*
* Statistics counters of the socket lists
@@ -1138,6 +1095,7 @@
{
int err;
struct socket *sock;
+ const struct net_proto_family *pf;
/*
* Check protocol is in range
@@ -1166,6 +1124,21 @@
if (err)
return err;
+ /*
+ * Allocate the socket and allow the family to set things up. if
+ * the protocol is 0, the family is instructed to select an appropriate
+ * default.
+ */
+ sock = sock_alloc();
+ if (!sock) {
+ if (net_ratelimit())
+ printk(KERN_WARNING "socket: no more sockets\n");
+ return -ENFILE; /* Not exactly a match, but its the
+ closest posix thing */
+ }
+
+ sock->type = type;
+
#if defined(CONFIG_KMOD)
/* Attempt to load a protocol module if the find failed.
*
@@ -1173,72 +1146,61 @@
* requested real, full-featured networking support upon configuration.
* Otherwise module support will break!
*/
- if (net_families[family] == NULL) {
+ if (net_families[family] == NULL)
request_module("net-pf-%d", family);
- }
#endif
- net_family_read_lock();
- if (net_families[family] == NULL) {
- err = -EAFNOSUPPORT;
- goto out;
- }
-
-/*
- * Allocate the socket and allow the family to set things up. if
- * the protocol is 0, the family is instructed to select an appropriate
- * default.
- */
-
- if (!(sock = sock_alloc())) {
- if (net_ratelimit())
- printk(KERN_WARNING "socket: no more sockets\n");
- err = -ENFILE; /* Not exactly a match, but its the
- closest posix thing */
- goto out;
- }
-
- sock->type = type;
+ rcu_read_lock();
+ pf = rcu_dereference(net_families[family]);
+ err = -EAFNOSUPPORT;
+ if (!pf)
+ goto out_release;
/*
* We will call the ->create function, that possibly is in a loadable
* module, so we have to bump that loadable module refcnt first.
*/
- err = -EAFNOSUPPORT;
- if (!try_module_get(net_families[family]->owner))
+ if (!try_module_get(pf->owner))
goto out_release;
- if ((err = net_families[family]->create(sock, protocol)) < 0) {
- sock->ops = NULL;
+ /* Now protected by module ref count */
+ rcu_read_unlock();
+
+ err = pf->create(sock, protocol);
+ if (err < 0)
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;
- }
+ if (!try_module_get(sock->ops->owner))
+ goto out_module_busy;
+
/*
* 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;
+ module_put(pf->owner);
err = security_socket_post_create(sock, family, type, protocol, kern);
if (err)
goto out_release;
+ *res = sock;
-out:
- net_family_read_unlock();
- return err;
+ return 0;
+
+out_module_busy:
+ err = -EAFNOSUPPORT;
out_module_put:
- module_put(net_families[family]->owner);
-out_release:
+ sock->ops = NULL;
+ module_put(pf->owner);
+out_sock_release:
sock_release(sock);
- goto out;
+ return err;
+
+out_release:
+ rcu_read_unlock();
+ goto out_sock_release;
}
int sock_create(int family, int type, int protocol, struct socket **res)
@@ -2109,12 +2071,15 @@
#endif /* __ARCH_WANT_SYS_SOCKETCALL */
-/*
+/**
+ * sock_register - add a socket protocol handler
+ * @ops: description of protocol
+ *
* This function is called by a protocol handler that wants to
* advertise its address family, and have it linked into the
- * SOCKET module.
+ * socket interface. The value ops->family coresponds to the
+ * socket system call protocol family.
*/
-
int sock_register(struct net_proto_family *ops)
{
int err;
@@ -2124,31 +2089,44 @@
NPROTO);
return -ENOBUFS;
}
- net_family_write_lock();
- err = -EEXIST;
- if (net_families[ops->family] == NULL) {
+
+ spin_lock(&net_family_lock);
+ if (net_families[ops->family])
+ err = -EEXIST;
+ else {
net_families[ops->family] = ops;
err = 0;
}
- net_family_write_unlock();
+ spin_unlock(&net_family_lock);
+
printk(KERN_INFO "NET: Registered protocol family %d\n", ops->family);
return err;
}
-/*
+/**
+ * sock_unregister - remove a protocol handler
+ * @family: protocol family to remove
+ *
* This function is called by a protocol handler that wants to
* remove its address family, and have it unlinked from the
- * SOCKET module.
+ * new socket creation.
+ *
+ * If protocol handler is a module, then it can use module reference
+ * counts to protect against new references. If protocol handler is not
+ * a module then it needs to provide its own protection in
+ * the ops->create routine.
*/
-
int sock_unregister(int family)
{
if (family < 0 || family >= NPROTO)
- return -1;
+ return -EINVAL;
- net_family_write_lock();
+ spin_lock(&net_family_lock);
net_families[family] = NULL;
- net_family_write_unlock();
+ spin_unlock(&net_family_lock);
+
+ synchronize_rcu();
+
printk(KERN_INFO "NET: Unregistered protocol family %d\n", family);
return 0;
}