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>

1 files changed, 7 insertions, 8 deletions

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;
 }