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;