• Sowmini Varadhan's avatar
    RDS: TCP: Synchronize accept() and connect() paths on t_conn_lock. · bd7c5f98
    Sowmini Varadhan authored
    An arbitration scheme for duelling SYNs is implemented as part of
    commit 241b2719 ("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: default avatarSowmini Varadhan <sowmini.varadhan@oracle.com>
    Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@oracle.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    bd7c5f98
tcp.c 15.6 KB