[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 #103 from Richard Scheffenegger <rscheff@freebsd.org> ---
(In reply to Marek Zarychta from comment #102)

This setting got enabled by default in D28702
(https://reviews.freebsd.org/rGd1de2b05a001d3d80f633f576f4909c2686dda3d).

Prior to this, RFC6675 (SACK loss recovery) was implemented more fully with
D18985
(https://reviews.freebsd.org/rG3c40e1d52cd86168779cf99dbabe58df465d7e3f).

This combination - enhanced features, combined with a very long lingering issue
in handling rare corner cases of SACK loss recovery & retransmission timeout
(RTO) interaction lead to the much higher incidence rate, and actual panics
reported in these three associated bugs.

As a part of the sequence of events which lead to this issue includes
non-responsive clients or network paths with extreme packet loss rates, this
effect is unlikely to be observed in stable, low loss, reactive client
environments.

Nevertheless, there is still a discussion point, if there should be a (binary)
patch for this - or if providing a patch, and including this in STABLE-13 /
STABLE-12 is sufficient. Most affected deployments could include the patches,
so far.

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