• Florian Westphal's avatar
    mptcp: break and restart in case mptcp sndbuf is full · fb529e62
    Florian Westphal authored
    Its not enough to check for available tcp send space.
    
    We also hold on to transmitted data for mptcp-level retransmits.
    Right now we will send more and more data if the peer can ack data
    at the tcp level fast enough, since that frees up tcp send buffer space.
    
    But we also need to check that data was acked and reclaimed at the mptcp
    level.
    
    Therefore add needed check in mptcp_sendmsg, flush tcp data and
    wait until more mptcp snd space becomes available if we are over the
    limit.  Before we wait for more data, also make sure we start the
    retransmit timer if we ran out of sndbuf space.
    
    Otherwise there is a very small chance that we wait forever:
    
     * receiver is waiting for data
     * sender is blocked because mptcp socket buffer is full
     * at tcp level, all data was acked
     * mptcp-level snd_una was not updated, because last ack
       that acknowledged the last data packet carried an older
       MPTCP-ack.
    
    Restarting the retransmit timer avoids this problem: if TCP
    subflow is idle, data is retransmitted from the RTX queue.
    
    New data will make the peer send a new, updated MPTCP-Ack.
    Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    fb529e62
protocol.c 48.9 KB