• Sowmini Varadhan's avatar
    RDS: Use a single TCP socket for both send and receive. · 3b20fc38
    Sowmini Varadhan authored
    Commit f711a6ae ("net/rds: RDS-TCP: Always create a new rds_sock
    for an incoming connection.") modified rds-tcp so that an incoming SYN
    would ignore an existing "client" TCP connection which had the local
    port set to the transient port.  The motivation for ignoring the existing
    "client" connection in f711a6ae was to avoid race conditions and an
    endless duel of reconnect attempts triggered by a restart/abort of one
    of the nodes in the TCP connection.
    
    However, having separate sockets for active and passive sides
    is avoidable, and the simpler model of a single TCP socket for
    both send and receives of all RDS connections associated with
    that tcp socket makes for easier observability. We avoid the race
    conditions from f711a6ae by attempting reconnects in rds_conn_shutdown
    if, and only if, the (new) c_outgoing bit is set for RDS_TRANS_TCP.
    The c_outgoing bit is initialized in __rds_conn_create().
    
    A side-effect of re-using the client rds_connection for an incoming
    SYN is the potential of encountering duelling SYNs, i.e., we
    have an outgoing RDS_CONN_CONNECTING socket when we get the incoming
    SYN. The logic to arbitrate this criss-crossing SYN exchange in
    rds_tcp_accept_one() has been modified to emulate the BGP state
    machine: the smaller IP address should back off from the connection attempt.
    Signed-off-by: default avatarSowmini Varadhan <sowmini.varadhan@oracle.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    3b20fc38
rds.h 25.1 KB