tcp: use SACKs and DSACKs that arrive on ACKs below snd_una
The bug: When the ACK field is below snd_una (which can happen when ACKs are reordered), senders ignored DSACKs (preventing undo) and did not call tcp_fastretrans_alert, so they did not increment prr_delivered to reflect newly-SACKed sequence ranges, and did not call tcp_xmit_retransmit_queue, thus passing up chances to send out more retransmitted and new packets based on any newly-SACKed packets. The change: When the ACK field is below snd_una (the "old_ack" goto label), call tcp_fastretrans_alert to allow undo based on any newly-arrived DSACKs and try to send out more packets based on newly-SACKed packets. Other patches in this series will provide other changes that are necessary to fully fix this problem. Signed-off-by: NNeal Cardwell <ncardwell@google.com> Acked-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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