net: Convert TCP/DCCP listening hash tables to use RCU
Eric Dumazet [Mon, 24 Nov 2008 01:22:55 +0000 (17:22 -0800)]
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
net/ipv4/inet_diag.c
net/ipv4/inet_hashtables.c
net/ipv4/tcp_ipv4.c
net/ipv6/inet6_hashtables.c

index ec7ee2e..f44bb5c 100644 (file)
@@ -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. */
index 998a78f..588a779 100644 (file)
@@ -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) {
index 4c273a9..11fcb87 100644 (file)
@@ -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);
index a81caa1..cab2458 100644 (file)
@@ -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;
index e0fd681..8fe267f 100644 (file)
@@ -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;
 }