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>

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) {

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

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;
 }