[PATCH net-next 1/4] tcp: use RCU in __inet{6}_check_established()

[Eric Dumazet <edumazet@google.com>]

When __inet_hash_connect() has to try many 4-tuples before
finding an available one, we see a high spinlock cost from
__inet_check_established() and/or __inet6_check_established().

This patch adds an RCU lookup to avoid the spinlock
acquisition when the 4-tuple is found in the hash table.

Note that there are still spin_lock_bh() calls in
__inet_hash_connect() to protect inet_bind_hashbucket,
this will be fixed later in this series.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
---
 net/ipv4/inet_hashtables.c  | 19 ++++++++++++++++---
 net/ipv6/inet6_hashtables.c | 19 ++++++++++++++++---
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 9bfcfd016e18275fb50fea8d77adc8a64fb12494..46d39aa2199ec3a405b50e8e85130e990d2c26b7 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -551,11 +551,24 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
 	unsigned int hash = inet_ehashfn(net, daddr, lport,
 					 saddr, inet->inet_dport);
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
-	spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
-	struct sock *sk2;
-	const struct hlist_nulls_node *node;
 	struct inet_timewait_sock *tw = NULL;
+	const struct hlist_nulls_node *node;
+	struct sock *sk2;
+	spinlock_t *lock;
+
+	rcu_read_lock();
+	sk_nulls_for_each(sk2, node, &head->chain) {
+		if (sk2->sk_hash != hash ||
+		    !inet_match(net, sk2, acookie, ports, dif, sdif))
+			continue;
+		if (sk2->sk_state == TCP_TIME_WAIT)
+			break;
+		rcu_read_unlock();
+		return -EADDRNOTAVAIL;
+	}
+	rcu_read_unlock();
 
+	lock = inet_ehash_lockp(hinfo, hash);
 	spin_lock(lock);
 
 	sk_nulls_for_each(sk2, node, &head->chain) {
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 9ec05e354baa69d14e88da37f5a9fce11e874e35..3604a5cae5d29a25d24f9513308334ff8e64b083 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -276,11 +276,24 @@ static int __inet6_check_established(struct inet_timewait_death_row *death_row,
 	const unsigned int hash = inet6_ehashfn(net, daddr, lport, saddr,
 						inet->inet_dport);
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
-	spinlock_t *lock = inet_ehash_lockp(hinfo, hash);
-	struct sock *sk2;
-	const struct hlist_nulls_node *node;
 	struct inet_timewait_sock *tw = NULL;
+	const struct hlist_nulls_node *node;
+	struct sock *sk2;
+	spinlock_t *lock;
+
+	rcu_read_lock();
+	sk_nulls_for_each(sk2, node, &head->chain) {
+		if (sk2->sk_hash != hash ||
+		    !inet6_match(net, sk2, saddr, daddr, ports, dif, sdif))
+			continue;
+		if (sk2->sk_state == TCP_TIME_WAIT)
+			break;
+		rcu_read_unlock();
+		return -EADDRNOTAVAIL;
+	}
+	rcu_read_unlock();
 
+	lock = inet_ehash_lockp(hinfo, hash);
 	spin_lock(lock);
 
 	sk_nulls_for_each(sk2, node, &head->chain) {
-- 
2.48.1.711.g2feabab25a-goog