net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls

RCU was added to UDP lookups, using a fast infrastructure :
- sockets kmem_cache use SLAB_DESTROY_BY_RCU and dont pay the
  price of call_rcu() at freeing time.
- hlist_nulls permits to use few memory barriers.

This patch uses same infrastructure for TCP/DCCP established
and timewait sockets.

Thanks to SLAB_DESTROY_BY_RCU, no slowdown for applications
using short lived TCP connections. A followup patch, converting
rwlocks to spinlocks will even speedup this case.

__inet_lookup_established() is pretty fast now we dont have to
dirty a contended cache line (read_lock/read_unlock)

Only established and timewait hashtable are converted to RCU
(bind table and listen table are still using traditional locking)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 55 insertions, 23 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index be41ebbec4eb..fd269cfef0ec 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -223,35 +223,65 @@ struct sock * __inet_lookup_established(struct net *net,
         INET_ADDR_COOKIE(acookie, saddr, daddr)
         const __portpair ports = INET_COMBINED_PORTS(sport, hnum);
         struct sock *sk;
-        const struct hlist_node *node;
+        const struct hlist_nulls_node *node;
         /* Optimize here for direct hit, only listening connections can
          * have wildcards anyways.
          */
         unsigned int hash = inet_ehashfn(net, daddr, hnum, saddr, sport);
-        struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
-        rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
+        unsigned int slot = hash & (hashinfo->ehash_size - 1);
+        struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
 
-        prefetch(head->chain.first);
-        read_lock(lock);
-        sk_for_each(sk, node, &head->chain) {
+        rcu_read_lock();
+begin:
+        sk_nulls_for_each_rcu(sk, node, &head->chain) {
                 if (INET_MATCH(sk, net, hash, acookie,
-                                        saddr, daddr, ports, dif))
-                        goto hit; /* You sunk my battleship! */
+                                        saddr, daddr, ports, dif)) {
+                        if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
+                                goto begintw;
+                        if (unlikely(!INET_MATCH(sk, net, hash, acookie,
+                                saddr, daddr, ports, dif))) {
+                                sock_put(sk);
+                                goto begin;
+                        }
+                        goto out;
+                }
         }
+        /*
+         * 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) != slot)
+                goto begin;
 
+begintw:
         /* Must check for a TIME_WAIT'er before going to listener hash. */
-        sk_for_each(sk, node, &head->twchain) {
+        sk_nulls_for_each_rcu(sk, node, &head->twchain) {
                 if (INET_TW_MATCH(sk, net, hash, acookie,
-                                        saddr, daddr, ports, dif))
-                        goto hit;
+                                        saddr, daddr, ports, dif)) {
+                        if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt))) {
+                                sk = NULL;
+                                goto out;
+                        }
+                        if (unlikely(!INET_TW_MATCH(sk, net, hash, acookie,
+                                 saddr, daddr, ports, dif))) {
+                                sock_put(sk);
+                                goto begintw;
+                        }
+                        goto out;
+                }
         }
+        /*
+         * 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) != slot)
+                goto begintw;
         sk = NULL;
 out:
-        read_unlock(lock);
+        rcu_read_unlock();
         return sk;
-hit:
-        sock_hold(sk);
-        goto out;
 }
 EXPORT_SYMBOL_GPL(__inet_lookup_established);
 
@@ -272,14 +302,14 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
         struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
         rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
         struct sock *sk2;
-        const struct hlist_node *node;
+        const struct hlist_nulls_node *node;
         struct inet_timewait_sock *tw;
 
         prefetch(head->chain.first);
         write_lock(lock);
 
         /* Check TIME-WAIT sockets first. */
-        sk_for_each(sk2, node, &head->twchain) {
+        sk_nulls_for_each(sk2, node, &head->twchain) {
                 tw = inet_twsk(sk2);
 
                 if (INET_TW_MATCH(sk2, net, hash, acookie,
@@ -293,7 +323,7 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
         tw = NULL;
 
         /* And established part... */
-        sk_for_each(sk2, node, &head->chain) {
+        sk_nulls_for_each(sk2, node, &head->chain) {
                 if (INET_MATCH(sk2, net, hash, acookie,
                                         saddr, daddr, ports, dif))
                         goto not_unique;
@@ -306,7 +336,7 @@ unique:
         inet->sport = htons(lport);
         sk->sk_hash = hash;
         WARN_ON(!sk_unhashed(sk));
-        __sk_add_node(sk, &head->chain);
+        __sk_nulls_add_node_rcu(sk, &head->chain);
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
         write_unlock(lock);
 
@@ -338,7 +368,7 @@ static inline u32 inet_sk_port_offset(const struct sock *sk)
 void __inet_hash_nolisten(struct sock *sk)
 {
         struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
-        struct hlist_head *list;
+        struct hlist_nulls_head *list;
         rwlock_t *lock;
         struct inet_ehash_bucket *head;
 
@@ -350,7 +380,7 @@ void __inet_hash_nolisten(struct sock *sk)
         lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 
         write_lock(lock);
-        __sk_add_node(sk, list);
+        __sk_nulls_add_node_rcu(sk, list);
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
         write_unlock(lock);
 }
@@ -400,13 +430,15 @@ void inet_unhash(struct sock *sk)
                 local_bh_disable();
                 inet_listen_wlock(hashinfo);
                 lock = &hashinfo->lhash_lock;
+                if (__sk_del_node_init(sk))
+                        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
         } else {
                 lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
                 write_lock_bh(lock);
+                if (__sk_nulls_del_node_init_rcu(sk))
+                        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
         }
 
-        if (__sk_del_node_init(sk))
-                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
         write_unlock_bh(lock);
 out:
         if (sk->sk_state == TCP_LISTEN)