bc9f38c832
Previously if an active TCP open has SYN timeout, it always undo the cwnd upon receiving the SYNACK. This is because tcp_clean_rtx_queue would reset tp->retrans_stamp when SYN is acked, which fools then tcp_try_undo_loss and tcp_packet_delayed. Addressing this issue is required to properly support undo for spurious SYN timeout. Fixing this is tricky -- for active TCP open tp->retrans_stamp records the time when the handshake starts, not the first retransmission time as the name may suggest. The simplest fix is for tcp_packet_delayed to ensure it is valid before comparing with other timestamp. One side effect of this change is active TCP Fast Open that incurred SYN timeout. Upon receiving a SYN-ACK that only acknowledged the SYN, it would immediately retransmit unacknowledged data in tcp_ack() because the data is marked lost after SYN timeout. But the retransmission would have an incorrect ack sequence number since rcv_nxt has not been updated yet tcp_rcv_synsent_state_process(), the retransmission needs to properly handed by tcp_rcv_fastopen_synack() like before. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.