[Bug 264257] [tcp] Panic: Fatal trap 12: page fault while in kernel mode (if_io_tqg_4) - m_copydata ... at /usr/src/sys/kern/uipc_mbuf.c:659

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=264257

--- Comment #55 from Richard Scheffenegger <rscheff@freebsd.org> ---
Thanks for the core. For stable operation, please use an unpatched kernel, and
without net.inet.tcp.rfc6675_pipe=0

The patched cores confirm that during the very final phases, the stack
increments one of the variables multiple times for the FIN bit, when it should
only have incremented it once. Together with SACK rescue retransmissions
(enabled by above sysctl) this leads to an attempt to send out non-existing
data.

the TCPPCAP and sudo syssctl net.inet.tcp.tcp_pcap_packets=10 would retain the
last 10 packets of every session in-memory, in order to create a reproduction
script, as the timing (relativ to retransmission timeouts, persist and
keepalive timers) of the clients packets apparently has something to do with
this problem.

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