net: convert TCP/DCCP ehash rwlocks to spinlocks

Now TCP & DCCP use RCU lookups, we can convert ehash rwlocks to spinlocks.

/proc/net/tcp and other seq_file 'readers' can safely be converted to 'writers'.

This should speedup writers, since spin_lock()/spin_unlock()
only use one atomic operation instead of two for write_lock()/write_unlock()

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

4 files changed, 34 insertions, 36 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 377d004e5723..4c273a9981a6 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -271,13 +271,12 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
         struct net *net = sock_net(sk);
         unsigned int hash = inet_ehashfn(net, daddr, lport, saddr, inet->dport);
         struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
-        rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
+        spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
         struct sock *sk2;
         const struct hlist_nulls_node *node;
         struct inet_timewait_sock *tw;
 
-        prefetch(head->chain.first);
-        write_lock(lock);
+        spin_lock(lock);
 
         /* Check TIME-WAIT sockets first. */
         sk_nulls_for_each(sk2, node, &head->twchain) {
@@ -308,8 +307,8 @@ unique:
         sk->sk_hash = hash;
         WARN_ON(!sk_unhashed(sk));
         __sk_nulls_add_node_rcu(sk, &head->chain);
+        spin_unlock(lock);
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
-        write_unlock(lock);
 
         if (twp) {
                 *twp = tw;
@@ -325,7 +324,7 @@ unique:
         return 0;
 
 not_unique:
-        write_unlock(lock);
+        spin_unlock(lock);
         return -EADDRNOTAVAIL;
 }
 
@@ -340,7 +339,7 @@ void __inet_hash_nolisten(struct sock *sk)
 {
         struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
         struct hlist_nulls_head *list;
-        rwlock_t *lock;
+        spinlock_t *lock;
         struct inet_ehash_bucket *head;
 
         WARN_ON(!sk_unhashed(sk));
@@ -350,10 +349,10 @@ void __inet_hash_nolisten(struct sock *sk)
         list = &head->chain;
         lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 
-        write_lock(lock);
+        spin_lock(lock);
         __sk_nulls_add_node_rcu(sk, list);
+        spin_unlock(lock);
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
-        write_unlock(lock);
 }
 EXPORT_SYMBOL_GPL(__inet_hash_nolisten);
 
@@ -402,12 +401,12 @@ void inet_unhash(struct sock *sk)
                         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
                 spin_unlock_bh(&ilb->lock);
         } else {
-                rwlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
+                spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 
-                write_lock_bh(lock);
+                spin_lock_bh(lock);
                 if (__sk_nulls_del_node_init_rcu(sk))
                         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-                write_unlock_bh(lock);
+                spin_unlock_bh(lock);
         }
 }
 EXPORT_SYMBOL_GPL(inet_unhash);
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 60689951ecdb..8554d0ea1719 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -20,16 +20,16 @@ static void __inet_twsk_kill(struct inet_timewait_sock *tw,
         struct inet_bind_hashbucket *bhead;
         struct inet_bind_bucket *tb;
         /* Unlink from established hashes. */
-        rwlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
+        spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
 
-        write_lock(lock);
+        spin_lock(lock);
         if (hlist_nulls_unhashed(&tw->tw_node)) {
-                write_unlock(lock);
+                spin_unlock(lock);
                 return;
         }
         hlist_nulls_del_rcu(&tw->tw_node);
         sk_nulls_node_init(&tw->tw_node);
-        write_unlock(lock);
+        spin_unlock(lock);
 
         /* Disassociate with bind bucket. */
         bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
@@ -76,7 +76,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
         const struct inet_sock *inet = inet_sk(sk);
         const struct inet_connection_sock *icsk = inet_csk(sk);
         struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
-        rwlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
+        spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
         struct inet_bind_hashbucket *bhead;
         /* Step 1: Put TW into bind hash. Original socket stays there too.
            Note, that any socket with inet->num != 0 MUST be bound in
@@ -90,7 +90,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
         inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
         spin_unlock(&bhead->lock);
 
-        write_lock(lock);
+        spin_lock(lock);
 
         /*
          * Step 2: Hash TW into TIMEWAIT chain.
@@ -104,7 +104,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
         if (__sk_nulls_del_node_init_rcu(sk))
                 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 
-        write_unlock(lock);
+        spin_unlock(lock);
 }
 
 EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);
@@ -427,9 +427,9 @@ void inet_twsk_purge(struct net *net, struct inet_hashinfo *hashinfo,
         for (h = 0; h < (hashinfo->ehash_size); h++) {
                 struct inet_ehash_bucket *head =
                         inet_ehash_bucket(hashinfo, h);
-                rwlock_t *lock = inet_ehash_lockp(hashinfo, h);
+                spinlock_t *lock = inet_ehash_lockp(hashinfo, h);
 restart:
-                write_lock(lock);
+                spin_lock(lock);
                 sk_nulls_for_each(sk, node, &head->twchain) {
 
                         tw = inet_twsk(sk);
@@ -438,13 +438,13 @@ restart:
                                 continue;
 
                         atomic_inc(&tw->tw_refcnt);
-                        write_unlock(lock);
+                        spin_unlock(lock);
                         inet_twsk_deschedule(tw, twdr);
                         inet_twsk_put(tw);
 
                         goto restart;
                 }
-                write_unlock(lock);
+                spin_unlock(lock);
         }
         local_bh_enable();
 }
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 330b08a12274..a81caa1be0cf 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1970,13 +1970,13 @@ static void *established_get_first(struct seq_file *seq)
                 struct sock *sk;
                 struct hlist_nulls_node *node;
                 struct inet_timewait_sock *tw;
-                rwlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
+                spinlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
 
                 /* Lockless fast path for the common case of empty buckets */
                 if (empty_bucket(st))
                         continue;
 
-                read_lock_bh(lock);
+                spin_lock_bh(lock);
                 sk_nulls_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
                         if (sk->sk_family != st->family ||
                             !net_eq(sock_net(sk), net)) {
@@ -1995,7 +1995,7 @@ static void *established_get_first(struct seq_file *seq)
                         rc = tw;
                         goto out;
                 }
-                read_unlock_bh(lock);
+                spin_unlock_bh(lock);
                 st->state = TCP_SEQ_STATE_ESTABLISHED;
         }
 out:
@@ -2023,7 +2023,7 @@ get_tw:
                         cur = tw;
                         goto out;
                 }
-                read_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
+                spin_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
                 st->state = TCP_SEQ_STATE_ESTABLISHED;
 
                 /* Look for next non empty bucket */
@@ -2033,7 +2033,7 @@ get_tw:
                 if (st->bucket >= tcp_hashinfo.ehash_size)
                         return NULL;
 
-                read_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
+                spin_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
                 sk = sk_nulls_head(&tcp_hashinfo.ehash[st->bucket].chain);
         } else
                 sk = sk_nulls_next(sk);
@@ -2134,7 +2134,7 @@ static void tcp_seq_stop(struct seq_file *seq, void *v)
         case TCP_SEQ_STATE_TIME_WAIT:
         case TCP_SEQ_STATE_ESTABLISHED:
                 if (v)
-                        read_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
+                        spin_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
                 break;
         }
 }
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 21544b9be259..e0fd68187f83 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -38,14 +38,14 @@ void __inet6_hash(struct sock *sk)
         } else {
                 unsigned int hash;
                 struct hlist_nulls_head *list;
-                rwlock_t *lock;
+                spinlock_t *lock;
 
                 sk->sk_hash = hash = inet6_sk_ehashfn(sk);
                 list = &inet_ehash_bucket(hashinfo, hash)->chain;
                 lock = inet_ehash_lockp(hashinfo, hash);
-                write_lock(lock);
+                spin_lock(lock);
                 __sk_nulls_add_node_rcu(sk, list);
-                write_unlock(lock);
+                spin_unlock(lock);
         }
 
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
@@ -195,13 +195,12 @@ static int __inet6_check_established(struct inet_timewait_death_row *death_row,
         const unsigned int hash = inet6_ehashfn(net, daddr, lport, saddr,
                                                 inet->dport);
         struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
-        rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
+        spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
         struct sock *sk2;
         const struct hlist_nulls_node *node;
         struct inet_timewait_sock *tw;
 
-        prefetch(head->chain.first);
-        write_lock(lock);
+        spin_lock(lock);
 
         /* Check TIME-WAIT sockets first. */
         sk_nulls_for_each(sk2, node, &head->twchain) {
@@ -230,8 +229,8 @@ unique:
         WARN_ON(!sk_unhashed(sk));
         __sk_nulls_add_node_rcu(sk, &head->chain);
         sk->sk_hash = hash;
+        spin_unlock(lock);
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
-        write_unlock(lock);
 
         if (twp != NULL) {
                 *twp = tw;
@@ -246,7 +245,7 @@ unique:
         return 0;
 
 not_unique:
-        write_unlock(lock);
+        spin_unlock(lock);
         return -EADDRNOTAVAIL;
 }