[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 #70 from Richard Scheffenegger <rscheff@freebsd.org> ---
(In reply to Christos Chatzaras from comment #68)

From the provided core:

snd_una: 2568161219
snd_nxt: 2568161624
snd_max: 2568161624
snd_fack: 2568161624 (!!)

so_snd: 403

snd_una + so_snd: 2568161622

 *tp->sackhint->nexthole
{start = 2568161219, end = 2568161623, rxmit = 2568161622, ...

This indicates, that the remote client SACKed the 2nd FIN bit (which apparently
was sent at sequence number 2568161624, not 2568161623 as expected).

The SACK for this 2nd FIN created a SACK scoreboard hole, which included the
sequence number of the 1st FIN bit - which does not exist in the socket
sendbuffer. Thus when trying to retransmit this non-existing byte, the panic
happens.

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