soreuseport: TCP/IPv6 implementation

Motivation for soreuseport would be something like a web server
binding to port 80 running with multiple threads, where each thread
might have it's own listener socket.  This could be done as an
alternative to other models: 1) have one listener thread which
dispatches completed connections to workers. 2) accept on a single
listener socket from multiple threads.  In case #1 the listener thread
can easily become the bottleneck with high connection turn-over rate.
In case #2, the proportion of connections accepted per thread tends
to be uneven under high connection load (assuming simple event loop:
while (1) { accept(); process() }, wakeup does not promote fairness
among the sockets.  We have seen the  disproportion to be as high
as 3:1 ratio between thread accepting most connections and the one
accepting the fewest.  With so_reusport the distribution is
uniform.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 33 insertions, 9 deletions

diff --git a/net/ipv6/inet6_connection_sock.c b/net/ipv6/inet6_connection_sock.c
index 30647857a375..e4297a393678 100644
--- a/net/ipv6/inet6_connection_sock.c
+++ b/net/ipv6/inet6_connection_sock.c
@@ -32,6 +32,9 @@ int inet6_csk_bind_conflict(const struct sock *sk,
 {
         const struct sock *sk2;
         const struct hlist_node *node;
+        int reuse = sk->sk_reuse;
+        int reuseport = sk->sk_reuseport;
+        int uid = sock_i_uid((struct sock *)sk);
 
         /* We must walk the whole port owner list in this case. -DaveM */
         /*
@@ -42,11 +45,17 @@ int inet6_csk_bind_conflict(const struct sock *sk,
                 if (sk != sk2 &&
                     (!sk->sk_bound_dev_if ||
                      !sk2->sk_bound_dev_if ||
-                     sk->sk_bound_dev_if == sk2->sk_bound_dev_if) &&
-                    (!sk->sk_reuse || !sk2->sk_reuse ||
-                     sk2->sk_state == TCP_LISTEN) &&
-                     ipv6_rcv_saddr_equal(sk, sk2))
-                        break;
+                     sk->sk_bound_dev_if == sk2->sk_bound_dev_if)) {
+                        if ((!reuse || !sk2->sk_reuse ||
+                             sk2->sk_state == TCP_LISTEN) &&
+                            (!reuseport || !sk2->sk_reuseport ||
+                             (sk2->sk_state != TCP_TIME_WAIT &&
+                              !uid_eq(uid,
+                                      sock_i_uid((struct sock *)sk2))))) {
+                                if (ipv6_rcv_saddr_equal(sk, sk2))
+                                        break;
+                        }
+                }
         }
 
         return node != NULL;
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index dea17fd28e50..32b4a1675d82 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -158,25 +158,38 @@ static inline int compute_score(struct sock *sk, struct net *net,
 }
 
 struct sock *inet6_lookup_listener(struct net *net,
-                struct inet_hashinfo *hashinfo, const struct in6_addr *daddr,
+                struct inet_hashinfo *hashinfo, const struct in6_addr *saddr,
+                const __be16 sport, const struct in6_addr *daddr,
                 const unsigned short hnum, const int dif)
 {
         struct sock *sk;
         const struct hlist_nulls_node *node;
         struct sock *result;
-        int score, hiscore;
+        int score, hiscore, matches = 0, reuseport = 0;
+        u32 phash = 0;
         unsigned int hash = inet_lhashfn(net, hnum);
         struct inet_listen_hashbucket *ilb = &hashinfo->listening_hash[hash];
 
         rcu_read_lock();
 begin:
         result = NULL;
-        hiscore = -1;
+        hiscore = 0;
         sk_nulls_for_each(sk, node, &ilb->head) {
                 score = compute_score(sk, net, hnum, daddr, dif);
                 if (score > hiscore) {
                         hiscore = score;
                         result = sk;
+                        reuseport = sk->sk_reuseport;
+                        if (reuseport) {
+                                phash = inet6_ehashfn(net, daddr, hnum,
+                                                      saddr, sport);
+                                matches = 1;
+                        }
+                } else if (score == hiscore && reuseport) {
+                        matches++;
+                        if (((u64)phash * matches) >> 32 == 0)
+                                result = sk;
+                        phash = next_pseudo_random32(phash);
                 }
         }
         /*
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 3701c3c6e2eb..06087e58738a 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -834,7 +834,8 @@ static void tcp_v6_send_reset(struct sock *sk, struct sk_buff *skb)
                  * no RST generated if md5 hash doesn't match.
                  */
                 sk1 = inet6_lookup_listener(dev_net(skb_dst(skb)->dev),
-                                           &tcp_hashinfo, &ipv6h->daddr,
+                                           &tcp_hashinfo, &ipv6h->saddr,
+                                           th->source, &ipv6h->daddr,
                                            ntohs(th->source), inet6_iif(skb));
                 if (!sk1)
                         return;
@@ -1598,6 +1599,7 @@ do_time_wait:
                 struct sock *sk2;
 
                 sk2 = inet6_lookup_listener(dev_net(skb->dev), &tcp_hashinfo,
+                                            &ipv6_hdr(skb)->saddr, th->source,
                                             &ipv6_hdr(skb)->daddr,
                                             ntohs(th->dest), inet6_iif(skb));
                 if (sk2 != NULL) {