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>

1 files changed, 14 insertions, 5 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;