netlink: eliminate nl_sk_hash_lock

As rhashtable_lookup_compare_insert() can guarantee the process
of search and insertion is atomic, it's safe to eliminate the
nl_sk_hash_lock. After this, object insertion or removal will
be protected with per bucket lock on write side while object
lookup is guarded with rcu read lock on read side.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 298e1df..01b702d 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -98,7 +98,7 @@ static void netlink_skb_destructor(struct sk_buff *skb);
 
 /* nl_table locking explained:
  * Lookup and traversal are protected with an RCU read-side lock. Insertion
- * and removal are protected with nl_sk_hash_lock while using RCU list
+ * and removal are protected with per bucket lock while using RCU list
  * modification primitives and may run in parallel to RCU protected lookups.
  * Destruction of the Netlink socket may only occur *after* nl_table_lock has
  * been acquired * either during or after the socket has been removed from
@@ -110,10 +110,6 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
-/* Protects netlink socket hash table mutations */
-DEFINE_MUTEX(nl_sk_hash_lock);
-EXPORT_SYMBOL_GPL(nl_sk_hash_lock);
-
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -998,6 +994,19 @@ static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
                                         &netlink_compare, &arg);
 }
 
+static bool __netlink_insert(struct netlink_table *table, struct sock *sk,
+                            struct net *net)
+{
+       struct netlink_compare_arg arg = {
+               .net = net,
+               .portid = nlk_sk(sk)->portid,
+       };
+
+       return rhashtable_lookup_compare_insert(&table->hash,
+                                               &nlk_sk(sk)->node,
+                                               &netlink_compare, &arg);
+}
+
 static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
        struct netlink_table *table = &nl_table[protocol];
@@ -1043,9 +1052,7 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
        struct netlink_table *table = &nl_table[sk->sk_protocol];
        int err = -EADDRINUSE;
 
-       mutex_lock(&nl_sk_hash_lock);
-       if (__netlink_lookup(table, portid, net))
-               goto err;
+       lock_sock(sk);
 
        err = -EBUSY;
        if (nlk_sk(sk)->portid)
@@ -1058,10 +1065,12 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 
        nlk_sk(sk)->portid = portid;
        sock_hold(sk);
-       rhashtable_insert(&table->hash, &nlk_sk(sk)->node);
-       err = 0;
+       if (__netlink_insert(table, sk, net))
+               err = 0;
+       else
+               sock_put(sk);
 err:
-       mutex_unlock(&nl_sk_hash_lock);
+       release_sock(sk);
        return err;
 }
 
@@ -1069,13 +1078,11 @@ static void netlink_remove(struct sock *sk)
 {
        struct netlink_table *table;
 
-       mutex_lock(&nl_sk_hash_lock);
        table = &nl_table[sk->sk_protocol];
        if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node)) {
                WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
                __sock_put(sk);
        }
-       mutex_unlock(&nl_sk_hash_lock);
 
        netlink_table_grab();
        if (nlk_sk(sk)->subscriptions) {

diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index fd96fa7..7518375 100644 (file)
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -74,6 +74,5 @@ struct netlink_table {
 
 extern struct netlink_table *nl_table;
 extern rwlock_t nl_table_lock;
-extern struct mutex nl_sk_hash_lock;
 
 #endif

diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index fcca36d..bb59a7e 100644 (file)
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -103,7 +103,7 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 {
        struct netlink_table *tbl = &nl_table[protocol];
        struct rhashtable *ht = &tbl->hash;
-       const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
+       const struct bucket_table *htbl = rht_dereference_rcu(ht->tbl, ht);
        struct net *net = sock_net(skb->sk);
        struct netlink_diag_req *req;
        struct netlink_sock *nlsk;
@@ -115,7 +115,7 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
        for (i = 0; i < htbl->size; i++) {
                struct rhash_head *pos;
 
-               rht_for_each_entry(nlsk, pos, htbl, i, node) {
+               rht_for_each_entry_rcu(nlsk, pos, htbl, i, node) {
                        sk = (struct sock *)nlsk;
 
                        if (!net_eq(sock_net(sk), net))
@@ -172,7 +172,7 @@ static int netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
 
        req = nlmsg_data(cb->nlh);
 
-       mutex_lock(&nl_sk_hash_lock);
+       rcu_read_lock();
        read_lock(&nl_table_lock);
 
        if (req->sdiag_protocol == NDIAG_PROTO_ALL) {
@@ -186,7 +186,7 @@ static int netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
        } else {
                if (req->sdiag_protocol >= MAX_LINKS) {
                        read_unlock(&nl_table_lock);
-                       mutex_unlock(&nl_sk_hash_lock);
+                       rcu_read_unlock();
                        return -ENOENT;
                }
 
@@ -194,7 +194,7 @@ static int netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
        }
 
        read_unlock(&nl_table_lock);
-       mutex_unlock(&nl_sk_hash_lock);
+       rcu_read_unlock();
 
        return skb->len;
 }