net: Convert TCP/DCCP listening hash tables to use RCU

This is the last step to be able to perform full RCU lookups
in __inet_lookup() : After established/timewait tables, we
add RCU lookups to listening hash table.

The only trick here is that a socket of a given type (TCP ipv4,
TCP ipv6, ...) can now flight between two different tables
(established and listening) during a RCU grace period, so we
must use different 'nulls' end-of-chain values for two tables.

We define a large value :

#define LISTENING_NULLS_BASE (1U << 29)

So that slots in listening table are guaranteed to have different
end-of-chain values than slots in established table. A reader can
still detect it finished its lookup in the right chain.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_hashtables.h

@@ -99,9 +99,16 @@ struct inet_bind_hashbucket {
 	struct hlist_head	chain;
 };
 
+/*
+ * Sockets can be hashed in established or listening table
+ * We must use different 'nulls' end-of-chain value for listening
+ * hash table, or we might find a socket that was closed and
+ * reallocated/inserted into established hash table
+ */
+#define LISTENING_NULLS_BASE (1U << 29)
 struct inet_listen_hashbucket {
 	spinlock_t		lock;
-	struct hlist_head	head;
+	struct hlist_nulls_head	head;
 };
 
 /* This is for listening sockets, thus all sockets which possess wildcards. */

net/ipv4/inet_diag.c

@@ -720,13 +720,13 @@ static int inet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
 
 		for (i = s_i; i < INET_LHTABLE_SIZE; i++) {
 			struct sock *sk;
-			struct hlist_node *node;
+			struct hlist_nulls_node *node;
 			struct inet_listen_hashbucket *ilb;
 
 			num = 0;
 			ilb = &hashinfo->listening_hash[i];
 			spin_lock_bh(&ilb->lock);
-			sk_for_each(sk, node, &ilb->head) {
+			sk_nulls_for_each(sk, node, &ilb->head) {
 				struct inet_sock *inet = inet_sk(sk);
 
 				if (num < s_num) {

net/ipv4/inet_hashtables.c

@@ -110,78 +110,79 @@ void __inet_inherit_port(struct sock *sk, struct sock *child)
 
 EXPORT_SYMBOL_GPL(__inet_inherit_port);
 
-/*
- * Don't inline this cruft. Here are some nice properties to exploit here. The
- * BSD API does not allow a listening sock to specify the remote port nor the
- * remote address for the connection. So always assume those are both
- * wildcarded during the search since they can never be otherwise.
- */
-static struct sock *inet_lookup_listener_slow(struct net *net,
-					      const struct hlist_head *head,
-					      const __be32 daddr,
-					      const unsigned short hnum,
+static inline int compute_score(struct sock *sk, struct net *net,
+				const unsigned short hnum, const __be32 daddr,
 				const int dif)
 {
-	struct sock *result = NULL, *sk;
-	const struct hlist_node *node;
-	int hiscore = -1;
-
-	sk_for_each(sk, node, head) {
-		const struct inet_sock *inet = inet_sk(sk);
+	int score = -1;
+	struct inet_sock *inet = inet_sk(sk);
 
 	if (net_eq(sock_net(sk), net) && inet->num == hnum &&
 			!ipv6_only_sock(sk)) {
-			const __be32 rcv_saddr = inet->rcv_saddr;
-			int score = sk->sk_family == PF_INET ? 1 : 0;
-
+		__be32 rcv_saddr = inet->rcv_saddr;
+		score = sk->sk_family == PF_INET ? 1 : 0;
 		if (rcv_saddr) {
 			if (rcv_saddr != daddr)
-					continue;
+				return -1;
 			score += 2;
 		}
 		if (sk->sk_bound_dev_if) {
 			if (sk->sk_bound_dev_if != dif)
-					continue;
+				return -1;
 			score += 2;
 		}
-			if (score == 5)
-				return sk;
-			if (score > hiscore) {
-				hiscore	= score;
-				result	= sk;
-			}
 	}
-	}
-	return result;
+	return score;
 }
 
-/* Optimize the common listener case. */
+/*
+ * Don't inline this cruft. Here are some nice properties to exploit here. The
+ * BSD API does not allow a listening sock to specify the remote port nor the
+ * remote address for the connection. So always assume those are both
+ * wildcarded during the search since they can never be otherwise.
+ */
+
+
 struct sock *__inet_lookup_listener(struct net *net,
 				    struct inet_hashinfo *hashinfo,
 				    const __be32 daddr, const unsigned short hnum,
 				    const int dif)
 {
-	struct sock *sk = NULL;
-	struct inet_listen_hashbucket *ilb;
+	struct sock *sk, *result;
+	struct hlist_nulls_node *node;
+	unsigned int hash = inet_lhashfn(net, hnum);
+	struct inet_listen_hashbucket *ilb = &hashinfo->listening_hash[hash];
+	int score, hiscore;
 
-	ilb = &hashinfo->listening_hash[inet_lhashfn(net, hnum)];
-	spin_lock(&ilb->lock);
-	if (!hlist_empty(&ilb->head)) {
-		const struct inet_sock *inet = inet_sk((sk = __sk_head(&ilb->head)));
-
-		if (inet->num == hnum && !sk->sk_node.next &&
-		    (!inet->rcv_saddr || inet->rcv_saddr == daddr) &&
-		    (sk->sk_family == PF_INET || !ipv6_only_sock(sk)) &&
-		    !sk->sk_bound_dev_if && net_eq(sock_net(sk), net))
-			goto sherry_cache;
-		sk = inet_lookup_listener_slow(net, &ilb->head, daddr, hnum, dif);
+	rcu_read_lock();
+begin:
+	result = NULL;
+	hiscore = -1;
+	sk_nulls_for_each_rcu(sk, node, &ilb->head) {
+		score = compute_score(sk, net, hnum, daddr, dif);
+		if (score > hiscore) {
+			result = sk;
+			hiscore = score;
 		}
-	if (sk) {
-sherry_cache:
-		sock_hold(sk);
 	}
-	spin_unlock(&ilb->lock);
-	return sk;
+	/*
+	 * if the nulls value we got at the end of this lookup is
+	 * not the expected one, we must restart lookup.
+	 * We probably met an item that was moved to another chain.
+	 */
+	if (get_nulls_value(node) != hash + LISTENING_NULLS_BASE)
+		goto begin;
+	if (result) {
+		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+			result = NULL;
+		else if (unlikely(compute_score(result, net, hnum, daddr,
+				  dif) < hiscore)) {
+			sock_put(result);
+			goto begin;
+		}
+	}
+	rcu_read_unlock();
+	return result;
 }
 EXPORT_SYMBOL_GPL(__inet_lookup_listener);
 
@@ -370,7 +371,7 @@ static void __inet_hash(struct sock *sk)
 	ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
 
 	spin_lock(&ilb->lock);
-	__sk_add_node(sk, &ilb->head);
+	__sk_nulls_add_node_rcu(sk, &ilb->head);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 	spin_unlock(&ilb->lock);
 }
@@ -388,26 +389,22 @@ EXPORT_SYMBOL_GPL(inet_hash);
 void inet_unhash(struct sock *sk)
 {
 	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
+	spinlock_t *lock;
+	int done;
 
 	if (sk_unhashed(sk))
 		return;
 
-	if (sk->sk_state == TCP_LISTEN) {
-		struct inet_listen_hashbucket *ilb;
-
-		ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
-		spin_lock_bh(&ilb->lock);
-		if (__sk_del_node_init(sk))
-			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-		spin_unlock_bh(&ilb->lock);
-	} else {
-		spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
+	if (sk->sk_state == TCP_LISTEN)
+		lock = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)].lock;
+	else
+		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 
 	spin_lock_bh(lock);
-		if (__sk_nulls_del_node_init_rcu(sk))
-			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
+	done =__sk_nulls_del_node_init_rcu(sk);
 	spin_unlock_bh(lock);
-	}
+	if (done)
+		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 }
 EXPORT_SYMBOL_GPL(inet_unhash);
 
@@ -526,8 +523,11 @@ void inet_hashinfo_init(struct inet_hashinfo *h)
 {
 	int i;
 
-	for (i = 0; i < INET_LHTABLE_SIZE; i++)
+	for (i = 0; i < INET_LHTABLE_SIZE; i++) {
 		spin_lock_init(&h->listening_hash[i].lock);
+		INIT_HLIST_NULLS_HEAD(&h->listening_hash[i].head,
+				      i + LISTENING_NULLS_BASE);
+		}
 }
 
 EXPORT_SYMBOL_GPL(inet_hashinfo_init);

net/ipv4/tcp_ipv4.c

@@ -1868,7 +1868,7 @@ static inline struct inet_timewait_sock *tw_next(struct inet_timewait_sock *tw)
 static void *listening_get_next(struct seq_file *seq, void *cur)
 {
 	struct inet_connection_sock *icsk;
-	struct hlist_node *node;
+	struct hlist_nulls_node *node;
 	struct sock *sk = cur;
 	struct inet_listen_hashbucket *ilb;
 	struct tcp_iter_state *st = seq->private;
@@ -1878,7 +1878,7 @@ static void *listening_get_next(struct seq_file *seq, void *cur)
 		st->bucket = 0;
 		ilb = &tcp_hashinfo.listening_hash[0];
 		spin_lock_bh(&ilb->lock);
-		sk = sk_head(&ilb->head);
+		sk = sk_nulls_head(&ilb->head);
 		goto get_sk;
 	}
 	ilb = &tcp_hashinfo.listening_hash[st->bucket];
@@ -1914,7 +1914,7 @@ get_req:
 		sk = sk_next(sk);
 	}
 get_sk:
-	sk_for_each_from(sk, node) {
+	sk_nulls_for_each_from(sk, node) {
 		if (sk->sk_family == st->family && net_eq(sock_net(sk), net)) {
 			cur = sk;
 			goto out;
@@ -1935,7 +1935,7 @@ start_req:
 	if (++st->bucket < INET_LHTABLE_SIZE) {
 		ilb = &tcp_hashinfo.listening_hash[st->bucket];
 		spin_lock_bh(&ilb->lock);
-		sk = sk_head(&ilb->head);
+		sk = sk_nulls_head(&ilb->head);
 		goto get_sk;
 	}
 	cur = NULL;

net/ipv6/inet6_hashtables.c

@@ -33,7 +33,7 @@ void __inet6_hash(struct sock *sk)
 
 		ilb = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
 		spin_lock(&ilb->lock);
-		__sk_add_node(sk, &ilb->head);
+		__sk_nulls_add_node_rcu(sk, &ilb->head);
 		spin_unlock(&ilb->lock);
 	} else {
 		unsigned int hash;
@@ -118,19 +118,13 @@ out:
 }
 EXPORT_SYMBOL(__inet6_lookup_established);
 
-struct sock *inet6_lookup_listener(struct net *net,
-		struct inet_hashinfo *hashinfo, const struct in6_addr *daddr,
-		const unsigned short hnum, const int dif)
+static int inline compute_score(struct sock *sk, struct net *net,
+				const unsigned short hnum,
+				const struct in6_addr *daddr,
+				const int dif)
 {
-	struct sock *sk;
-	const struct hlist_node *node;
-	struct sock *result = NULL;
-	int score, hiscore = 0;
-	struct inet_listen_hashbucket *ilb;
+	int score = -1;
 
-	ilb = &hashinfo->listening_hash[inet_lhashfn(net, hnum)];
-	spin_lock(&ilb->lock);
-	sk_for_each(sk, node, &ilb->head) {
 	if (net_eq(sock_net(sk), net) && inet_sk(sk)->num == hnum &&
 	    sk->sk_family == PF_INET6) {
 		const struct ipv6_pinfo *np = inet6_sk(sk);
@@ -138,27 +132,57 @@ struct sock *inet6_lookup_listener(struct net *net,
 		score = 1;
 		if (!ipv6_addr_any(&np->rcv_saddr)) {
 			if (!ipv6_addr_equal(&np->rcv_saddr, daddr))
-					continue;
+				return -1;
 			score++;
 		}
 		if (sk->sk_bound_dev_if) {
 			if (sk->sk_bound_dev_if != dif)
-					continue;
+				return -1;
 			score++;
 		}
-			if (score == 3) {
-				result = sk;
-				break;
 	}
+	return score;
+}
+
+struct sock *inet6_lookup_listener(struct net *net,
+		struct inet_hashinfo *hashinfo, const struct in6_addr *daddr,
+		const unsigned short hnum, const int dif)
+{
+	struct sock *sk;
+	const struct hlist_nulls_node *node;
+	struct sock *result;
+	int score, hiscore;
+	unsigned int hash = inet_lhashfn(net, hnum);
+	struct inet_listen_hashbucket *ilb = &hashinfo->listening_hash[hash];
+
+	rcu_read_lock();
+begin:
+	result = NULL;
+	hiscore = -1;
+	sk_nulls_for_each(sk, node, &ilb->head) {
+		score = compute_score(sk, net, hnum, daddr, dif);
 		if (score > hiscore) {
 			hiscore = score;
 			result = sk;
 		}
 	}
+	/*
+	 * if the nulls value we got at the end of this lookup is
+	 * not the expected one, we must restart lookup.
+	 * We probably met an item that was moved to another chain.
+	 */
+	if (get_nulls_value(node) != hash + LISTENING_NULLS_BASE)
+		goto begin;
+	if (result) {
+		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+			result = NULL;
+		else if (unlikely(compute_score(result, net, hnum, daddr,
+				  dif) < hiscore)) {
+			sock_put(result);
+			goto begin;
 		}
-	if (result)
-		sock_hold(result);
-	spin_unlock(&ilb->lock);
+	}
+	rcu_read_unlock();
 	return result;
 }