net/rds: RDS-TCP: Always create a new rds_sock for an incoming connection.

When running RDS over TCP, the active (client) side connects to the
listening ("passive") side at the RDS_TCP_PORT.  After the connection
is established, if the client side reboots (potentially without even
sending a FIN) the server still has a TCP socket in the esablished
state.  If the server-side now gets a new SYN comes from the client
with a different client port, TCP will create a new socket-pair, but
the RDS layer will incorrectly pull up the old rds_connection (which
is still associated with the stale t_sock and RDS socket state).

This patch corrects this behavior by having rds_tcp_accept_one()
always create a new connection for an incoming TCP SYN.
The rds and tcp state associated with the old socket-pair is cleaned
up via the rds_tcp_state_change() callback which would typically be
invoked in most cases when the client-TCP sends a FIN on TCP restart,
triggering a transition to CLOSE_WAIT state. In the rarer event of client
death without a FIN, TCP_KEEPALIVE probes on the socket will detect
the stale socket, and the TCP transition to CLOSE state will trigger
the RDS state cleanup.

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

3 files changed, 51 insertions, 0 deletions

diff --git a/net/rds/connection.c b/net/rds/connection.c
index 14f041398ca1..60f0cd6ed15f 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -126,7 +126,10 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
         struct rds_transport *loop_trans;
         unsigned long flags;
         int ret;
+        struct rds_transport *otrans = trans;
 
+        if (!is_outgoing && otrans->t_type == RDS_TRANS_TCP)
+                goto new_conn;
         rcu_read_lock();
         conn = rds_conn_lookup(head, laddr, faddr, trans);
         if (conn && conn->c_loopback && conn->c_trans != &rds_loop_transport &&
@@ -142,6 +145,7 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
         if (conn)
                 goto out;
 
+new_conn:
         conn = kmem_cache_zalloc(rds_conn_slab, gfp);
         if (!conn) {
                 conn = ERR_PTR(-ENOMEM);
diff --git a/net/rds/tcp_connect.c b/net/rds/tcp_connect.c
index f9f564a6c960..973109c7b8e8 100644
--- a/net/rds/tcp_connect.c
+++ b/net/rds/tcp_connect.c
@@ -62,6 +62,7 @@ void rds_tcp_state_change(struct sock *sk)
                 case TCP_ESTABLISHED:
                         rds_connect_complete(conn);
                         break;
+                case TCP_CLOSE_WAIT:
                 case TCP_CLOSE:
                         rds_conn_drop(conn);
                 default:
diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index 23ab4dcd1d9f..0da49e34495f 100644
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -45,12 +45,45 @@ static void rds_tcp_accept_worker(struct work_struct *work);
 static DECLARE_WORK(rds_tcp_listen_work, rds_tcp_accept_worker);
 static struct socket *rds_tcp_listen_sock;
 
+static int rds_tcp_keepalive(struct socket *sock)
+{
+        /* values below based on xs_udp_default_timeout */
+        int keepidle = 5; /* send a probe 'keepidle' secs after last data */
+        int keepcnt = 5; /* number of unack'ed probes before declaring dead */
+        int keepalive = 1;
+        int ret = 0;
+
+        ret = kernel_setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE,
+                                (char *)&keepalive, sizeof(keepalive));
+        if (ret < 0)
+                goto bail;
+
+        ret = kernel_setsockopt(sock, IPPROTO_TCP, TCP_KEEPCNT,
+                                (char *)&keepcnt, sizeof(keepcnt));
+        if (ret < 0)
+                goto bail;
+
+        ret = kernel_setsockopt(sock, IPPROTO_TCP, TCP_KEEPIDLE,
+                                (char *)&keepidle, sizeof(keepidle));
+        if (ret < 0)
+                goto bail;
+
+        /* KEEPINTVL is the interval between successive probes. We follow
+         * the model in xs_tcp_finish_connecting() and re-use keepidle.
+         */
+        ret = kernel_setsockopt(sock, IPPROTO_TCP, TCP_KEEPINTVL,
+                                (char *)&keepidle, sizeof(keepidle));
+bail:
+        return ret;
+}
+
 static int rds_tcp_accept_one(struct socket *sock)
 {
         struct socket *new_sock = NULL;
         struct rds_connection *conn;
         int ret;
         struct inet_sock *inet;
+        struct rds_tcp_connection *rs_tcp;
 
         ret = sock_create_lite(sock->sk->sk_family, sock->sk->sk_type,
                                sock->sk->sk_protocol, &new_sock);
@@ -63,6 +96,10 @@ static int rds_tcp_accept_one(struct socket *sock)
         if (ret < 0)
                 goto out;
 
+        ret = rds_tcp_keepalive(new_sock);
+        if (ret < 0)
+                goto out;
+
         rds_tcp_tune(new_sock);
 
         inet = inet_sk(new_sock->sk);
@@ -77,6 +114,15 @@ static int rds_tcp_accept_one(struct socket *sock)
                 ret = PTR_ERR(conn);
                 goto out;
         }
+        /* An incoming SYN request came in, and TCP just accepted it.
+         * We always create a new conn for listen side of TCP, and do not
+         * add it to the c_hash_list.
+         *
+         * If the client reboots, this conn will need to be cleaned up.
+         * rds_tcp_state_change() will do that cleanup
+         */
+        rs_tcp = (struct rds_tcp_connection *)conn->c_transport_data;
+        WARN_ON(!rs_tcp || rs_tcp->t_sock);
 
         /*
          * see the comment above rds_queue_delayed_reconnect()