06May2021 [FreeBSD WIKI]

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Attendees:  jtl@, rscheff@, tuexen@, rrs@

====== Discussion ======
  * [[https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=252913|PR 252913]]: tuexen@ got a tracefile and some information from Netflix. This impacts stable/12. rrs@ will commit an update to RACK in main and MFC to stable/13. We don't plan to fix this bug in stable/12.
    * Actually, we probably should deprecate (and even remove) RACK code from stable/12. However, we do think we can maintain RACK code throughout stable/13 support cycle.
    * Will update tcp(4) and tcp_bbr(4) man pages, and write a new man page for RACK, to note whether stacks are experimental or supported.

  * [[https://reviews.freebsd.org/D23230|D23230]]: ECN++, rscheff@ updated the sysctl interface so sysctls are not checked in fast path. Needs review.

  * [[https://reviews.freebsd.org/D28702|D28702]]: Closed.

  * [[https://reviews.freebsd.org/D29835|D29835]]: Closed.

  * Lost retransmission detection: [[https://reviews.freebsd.org/D28931|D28931]] is an idea for doing SACK loss recovery in the base stack. (Documented in an [[https://datatracker.ietf.org/doc/draft-scheffenegger-tcpm-lrd/|I-D]].) We discussed the idea further. rscheff@ will modify code to include a sysctl to enable/disable the new behavior.
    * Will be off by default.
    * Consensus: add socket option to control on a per-socket basis and add some basic statistics. rrs@ will review. The plan is to commit this before the next meeting.

  * [[https://reviews.freebsd.org/D29515|D29515]]: rscheff@ committed change to use jenkins hash with random salt and allow an administrator to re-salt with a sysctl. rscheff@ did MFC to stable/13. Closed.

  * tuexen@ committed support for TCP over UDP to main. He plans to MFC to stable/13. tuexen@ did this. Closed.

  * RACK, BBR, etc. will be updated. rrs@ will commit this week.
    * Plan is to MFC to stable/13. See above.

  * [[https://reviews.freebsd.org/D29411|D29411]], [[https://reviews.freebsd.org/D29440|D29440]]: Closed.
  * [[https://reviews.freebsd.org/D29441|D29441]], [[https://reviews.freebsd.org/D28822|D28822]]: PRR-related reviews still open. No plans to MFC D28822.

  * [[https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254725|254725]]: LRO panic. Peer ACKs up to last data byte. Peer SACKs FIN - see reconstructed trace from in-core packet headers {{TransportProtocols/06May2021/PR254725.trc?linkonly|PR254725.trc}}. snd_una is correct, but send buffer is empty. Still no progress on reproduction. Randall suggested changing the code to wait to send FIN until there was nothing outstanding (see [[https://reviews.freebsd.org/D29565|D29565]]). This change will delay the remote side recognizing session shutdown, which might impact applications which take action when a session closes. General consensus is that it would be better to find and fix the bugs.
    * User did not feel that they could afford downtime to reproduce. Will need to await a reproduction.

  * Follow up on the RST issue reported by NFS developer: We send a challenge ACK. Remote side sends a RST. We don't process the RST. rscheff@ proposed [[https://reviews.freebsd.org/D29690|D29690]]. tuexen@ and jtl@ have a small concern that we should do more work on finding the root cause before we commit a fix. rscheff@ will debug further on a machine seeing this problem.
    * Will ask Rick to reproduce and help us figure out the kernel state when we are rejecting the RST.

Next meeting: 20 May @ 1400 UTC