[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>

1 files changed, 76 insertions, 98 deletions

diff --git a/net/socket.c b/net/socket.c
index 156f2efa4e4a..b5a3fcb9ed6d 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 @@ static struct file_operations socket_file_ops = {
  *      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 @@ static int __sock_create(int family, int type, int protocol,
 {
         int err;
         struct socket *sock;
+        const struct net_proto_family *pf;
 
         /*
          *      Check protocol is in range
@@ -1166,6 +1124,21 @@ static int __sock_create(int family, int type, int protocol,
         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 @@ static int __sock_create(int family, int type, int protocol,
          * 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 @@ asmlinkage long sys_socketcall(int call, unsigned long __user *args)
 
 #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 @@ int sock_register(struct net_proto_family *ops)
                        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;
 }