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.

Details

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.

Diff Detail

Repository

rG FreeBSD src repository

Lint

Lint Passed

Unit

No Test Coverage

Build Status

Buildable 65950
Build 62833: arc lint + arc unit

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