tcp: ensure that SACK hole->rxmit never ends up left of the hole with LRD
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Authored by rscheff on Aug 4 2025, 7:34 PM.

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Reviewers

tuexen
cc

Group Reviewers

transport

Commits

rG7b9f6ebb9268: tcp: ensure SACK rxmit never ends up left of its hole
rG65d4a8339984: tcp: ensure SACK rxmit never ends up left of its hole

Summary

When a RTO happens during SACK loss recovery, snd_recover can possibly pulled left.
With Lost Retransmission Detection (LRD) this can lead to rxmit of a hole to end up
pointing to the left of the hole, which is unexpected and leads to complications.

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Repository

rG FreeBSD src repository

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Tests Not Applicable

Event Timeline

rscheff created this revision.Aug 4 2025, 7:34 PM

Herald added a reviewer: transport. · View Herald TranscriptAug 4 2025, 7:34 PM

Herald added subscribers: glebius, melifaro, imp. · View Herald Transcript

Harbormaster completed remote builds in B65950: Diff 159717.Aug 4 2025, 7:34 PM

rscheff requested review of this revision.Aug 4 2025, 7:34 PM

tuexen accepted this revision.Aug 4 2025, 7:52 PM

This revision is now accepted and ready to land.Aug 4 2025, 7:52 PM

I am ok with this patch. But I want to be sure how snd_recover shrinks. Is it because tp->snd_recover = tp->snd_recover_prev in CC_RTO_ERR? But that shall not be in SACK recovery.

Closed by commit rG65d4a8339984: tcp: ensure SACK rxmit never ends up left of its hole (authored by rscheff). · Explain WhyAug 6 2025, 9:50 PM

This revision was automatically updated to reflect the committed changes.

rscheff added a commit: rG65d4a8339984: tcp: ensure SACK rxmit never ends up left of its hole.

rscheff added a commit: rG7b9f6ebb9268: tcp: ensure SACK rxmit never ends up left of its hole.Aug 13 2025, 7:22 PM