RDS: TCP: Synchronize accept() and connect() paths on t_conn_lock.

An arbitration scheme for duelling SYNs is implemented as part of
commit 241b271952eb ("RDS-TCP: Reset tcp callbacks if re-using an
outgoing socket in rds_tcp_accept_one()") which ensures that both nodes
involved will arrive at the same arbitration decision. However, this
needs to be synchronized with an outgoing SYN to be generated by
rds_tcp_conn_connect(). This commit achieves the synchronization
through the t_conn_lock mutex in struct rds_tcp_connection.

The rds_conn_state is checked in rds_tcp_conn_connect() after acquiring
the t_conn_lock mutex.  A SYN is sent out only if the RDS connection is
not already UP (an UP would indicate that rds_tcp_accept_one() has
completed 3WH, so no SYN needs to be generated).

Similarly, the rds_conn_state is checked in rds_tcp_accept_one() after
acquiring the t_conn_lock mutex. The only acceptable states (to
allow continuation of the arbitration logic) are UP (i.e., outgoing SYN
was SYN-ACKed by peer after it sent us the SYN) or CONNECTING (we sent
outgoing SYN before we saw incoming SYN).

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/net/rds/tcp_connect.c b/net/rds/tcp_connect.c
index 5cb1687..49a3fcf 100644
--- a/net/rds/tcp_connect.c
+++ b/net/rds/tcp_connect.c
@@ -78,7 +78,14 @@ int rds_tcp_conn_connect(struct rds_connection *conn)
 	struct socket *sock = NULL;
 	struct sockaddr_in src, dest;
 	int ret;
+	struct rds_tcp_connection *tc = conn->c_transport_data;
+
+	mutex_lock(&tc->t_conn_lock);
 
+	if (rds_conn_up(conn)) {
+		mutex_unlock(&tc->t_conn_lock);
+		return 0;
+	}
 	ret = sock_create_kern(rds_conn_net(conn), PF_INET,
 			       SOCK_STREAM, IPPROTO_TCP, &sock);
 	if (ret < 0)
@@ -120,6 +127,7 @@ int rds_tcp_conn_connect(struct rds_connection *conn)
 	}
 
 out:
+	mutex_unlock(&tc->t_conn_lock);
 	if (sock)
 		sock_release(sock);
 	return ret;