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>

5 files changed, 147 insertions, 116 deletions

diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index ec7ee2e46d8c..f44bb5c77a70 100644
--- a/include/net/inet_hashtables.h
+++ b/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. */
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 998a78f169ff..588a7796e3e3 100644
--- a/net/ipv4/inet_diag.c
+++ b/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) {
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 4c273a9981a6..11fcb87a1fdd 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/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);
 
+static inline int compute_score(struct sock *sk, struct net *net,
+                                const unsigned short hnum, const __be32 daddr,
+                                const int dif)
+{
+        int score = -1;
+        struct inet_sock *inet = inet_sk(sk);
+
+        if (net_eq(sock_net(sk), net) && inet->num == hnum &&
+                        !ipv6_only_sock(sk)) {
+                __be32 rcv_saddr = inet->rcv_saddr;
+                score = sk->sk_family == PF_INET ? 1 : 0;
+                if (rcv_saddr) {
+                        if (rcv_saddr != daddr)
+                                return -1;
+                        score += 2;
+                }
+                if (sk->sk_bound_dev_if) {
+                        if (sk->sk_bound_dev_if != dif)
+                                return -1;
+                        score += 2;
+                }
+        }
+        return score;
+}
+
 /*
  * 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,
-                                              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);
-
-                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;
-
-                        if (rcv_saddr) {
-                                if (rcv_saddr != daddr)
-                                        continue;
-                                score += 2;
-                        }
-                        if (sk->sk_bound_dev_if) {
-                                if (sk->sk_bound_dev_if != dif)
-                                        continue;
-                                score += 2;
-                        }
-                        if (score == 5)
-                                return sk;
-                        if (score > hiscore) {
-                                hiscore = score;
-                                result  = sk;
-                        }
-                }
-        }
-        return result;
-}
 
-/* Optimize the common listener case. */
+
 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);
+        /*
+         * 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;
+                }
         }
-        spin_unlock(&ilb->lock);
-        return sk;
+        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;
+        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);
 
-                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);
-
-                spin_lock_bh(lock);
-                if (__sk_nulls_del_node_init_rcu(sk))
-                        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-                spin_unlock_bh(lock);
-        }
+        spin_lock_bh(lock);
+        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);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a81caa1be0cf..cab2458f86fd 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/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;
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index e0fd68187f83..8fe267feb81e 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/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;
@@ -118,47 +118,71 @@ out:
 }
 EXPORT_SYMBOL(__inet6_lookup_established);
 
+static int inline compute_score(struct sock *sk, struct net *net,
+                                const unsigned short hnum,
+                                const struct in6_addr *daddr,
+                                const int dif)
+{
+        int score = -1;
+
+        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);
+
+                score = 1;
+                if (!ipv6_addr_any(&np->rcv_saddr)) {
+                        if (!ipv6_addr_equal(&np->rcv_saddr, daddr))
+                                return -1;
+                        score++;
+                }
+                if (sk->sk_bound_dev_if) {
+                        if (sk->sk_bound_dev_if != dif)
+                                return -1;
+                        score++;
+                }
+        }
+        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_node *node;
-        struct sock *result = NULL;
-        int score, hiscore = 0;
-        struct inet_listen_hashbucket *ilb;
-
-        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);
-
-                        score = 1;
-                        if (!ipv6_addr_any(&np->rcv_saddr)) {
-                                if (!ipv6_addr_equal(&np->rcv_saddr, daddr))
-                                        continue;
-                                score++;
-                        }
-                        if (sk->sk_bound_dev_if) {
-                                if (sk->sk_bound_dev_if != dif)
-                                        continue;
-                                score++;
-                        }
-                        if (score == 3) {
-                                result = sk;
-                                break;
-                        }
-                        if (score > hiscore) {
-                                hiscore = score;
-                                result = 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 (result)
-                sock_hold(result);
-        spin_unlock(&ilb->lock);
+        /*
+         * 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;
 }