[Bug 253848] [tcp] panic: sackhint bytes rtx >= 0

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Fri Mar 5 17:35:20 UTC 2021


--- Comment #6 from Richard Scheffenegger <rscheff at freebsd.org> ---
It turned out that only under a specific set of circumstances - RTO during a
SACK loss recovery, while the client had not yet fully reported back all SACK
blocks - a unnecessary initialization of sack_bytes_rexmit caused this panic. 

In mundane environments this was virtually not reproduceable, and even in
exposed environments, tcp sessions apparently need to suffer from sudden RTT
jumps / path changes to elicit the panic.

Thanks to rrs@ and gallatin@ for helping by providing crucial timing and packet
trace/tcp state information around a few occurances.

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