1 files changed, 75 insertions, 3 deletions

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 86187dad1440..74ee126a6fe6 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -126,9 +126,81 @@ void rds_tcp_restore_callbacks(struct socket *sock,
 }
 
 /*
- * This is the only path that sets tc->t_sock.  Send and receive trust that
- * it is set.  The RDS_CONN_UP bit protects those paths from being
- * called while it isn't set.
+ * rds_tcp_reset_callbacks() switches the to the new sock and
+ * returns the existing tc->t_sock.
+ *
+ * The only functions that set tc->t_sock are rds_tcp_set_callbacks
+ * and rds_tcp_reset_callbacks.  Send and receive trust that
+ * it is set.  The absence of RDS_CONN_UP bit protects those paths
+ * from being called while it isn't set.
+ */
+void rds_tcp_reset_callbacks(struct socket *sock,
+                             struct rds_connection *conn)
+{
+        struct rds_tcp_connection *tc = conn->c_transport_data;
+        struct socket *osock = tc->t_sock;
+
+        if (!osock)
+                goto newsock;
+
+        /* Need to resolve a duelling SYN between peers.
+         * We have an outstanding SYN to this peer, which may
+         * potentially have transitioned to the RDS_CONN_UP state,
+         * so we must quiesce any send threads before resetting
+         * c_transport_data. We quiesce these threads by setting
+         * c_state to something other than RDS_CONN_UP, and then
+         * waiting for any existing threads in rds_send_xmit to
+         * complete release_in_xmit(). (Subsequent threads entering
+         * rds_send_xmit() will bail on !rds_conn_up().
+         *
+         * However an incoming syn-ack at this point would end up
+         * marking the conn as RDS_CONN_UP, and would again permit
+         * rds_send_xmi() threads through, so ideally we would
+         * synchronize on RDS_CONN_UP after lock_sock(), but cannot
+         * do that: waiting on !RDS_IN_XMIT after lock_sock() may
+         * end up deadlocking with tcp_sendmsg(), and the RDS_IN_XMIT
+         * would not get set. As a result, we set c_state to
+         * RDS_CONN_RESETTTING, to ensure that rds_tcp_state_change
+         * cannot mark rds_conn_path_up() in the window before lock_sock()
+         */
+        atomic_set(&conn->c_state, RDS_CONN_RESETTING);
+        wait_event(conn->c_waitq, !test_bit(RDS_IN_XMIT, &conn->c_flags));
+        lock_sock(osock->sk);
+        /* reset receive side state for rds_tcp_data_recv() for osock  */
+        if (tc->t_tinc) {
+                rds_inc_put(&tc->t_tinc->ti_inc);
+                tc->t_tinc = NULL;
+        }
+        tc->t_tinc_hdr_rem = sizeof(struct rds_header);
+        tc->t_tinc_data_rem = 0;
+        tc->t_sock = NULL;
+
+        write_lock_bh(&osock->sk->sk_callback_lock);
+
+        osock->sk->sk_user_data = NULL;
+        osock->sk->sk_data_ready = tc->t_orig_data_ready;
+        osock->sk->sk_write_space = tc->t_orig_write_space;
+        osock->sk->sk_state_change = tc->t_orig_state_change;
+        write_unlock_bh(&osock->sk->sk_callback_lock);
+        release_sock(osock->sk);
+        sock_release(osock);
+newsock:
+        rds_send_reset(conn);
+        lock_sock(sock->sk);
+        write_lock_bh(&sock->sk->sk_callback_lock);
+        tc->t_sock = sock;
+        sock->sk->sk_user_data = conn;
+        sock->sk->sk_data_ready = rds_tcp_data_ready;
+        sock->sk->sk_write_space = rds_tcp_write_space;
+        sock->sk->sk_state_change = rds_tcp_state_change;
+
+        write_unlock_bh(&sock->sk->sk_callback_lock);
+        release_sock(sock->sk);
+}
+
+/* Add tc to rds_tcp_tc_list and set tc->t_sock. See comments
+ * above rds_tcp_reset_callbacks for notes about synchronization
+ * with data path
  */
 void rds_tcp_set_callbacks(struct socket *sock, struct rds_connection *conn)
 {