Don't block on channel arbitator startup #9324

ziggie1984 · 2024-11-29T23:43:29Z

Replaces #9262

Fixes: #9323

coderabbitai · 2024-11-29T23:43:36Z

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guggero

Thanks a lot for looking into this. I think we can simplify the code somewhat and also reduce the number of goroutines a bit, see inline comment.

docs/release-notes/release-notes-0.19.0.md

contractcourt/chain_arbitrator.go

yyforyongyu

Left some comments here, I don't think the fix should happen in lnd. From the logs, what happened was the chan newInputs was blocked since we sent two inputs during the startup, and the first input was blocking on aux.ExtraBudgetForInputs,

2024-11-29 10:15:07.185 [INF] SWPR: Sweep request received: out_point=e4a01568a0cd879df94cd6c9ae8143e1304bf1731ddee7003c6f12df4f7baf13:0, witness_type=TaprootAnchorSweepSpend, relative_time_lock=0, absolute_time_lock=0, amount=0.00000330 BTC, parent=(<nil>), 
...
2024-11-29 10:15:07.192 [INF] CNCT: ChannelArbitrator(ce3ab677a419e40558d095faf7165ba143467c1dc5691632ad511224473eabc9:0): offering anchor from local commitment 7a4c66554f168a903202ed29e2a13e1061b8c0f484a4be7a2ef8d69ceac382c5:1 to sweeper with deadline=None, budget=0.00000330 BTC
2024-11-29 10:15:07.192 [INF] SWPR: Sweep request received: out_point=7a4c66554f168a903202ed29e2a13e1061b8c0f484a4be7a2ef8d69ceac382c5:1, witness_type=TaprootAnchorSweepSpend, relative_time_lock=0, absolute_time_lock=0, amount=0.00000330 BTC, parent=(fee=0.00001366 BTC, weight=958 wu), params=(startingFeeRate={false 0}, immediate=false, exclusive_group=948947804208955392, budget=0.00000330 BTC, deadline=none)

There are multiple ways we can fix this,

make newInputs a buffered chan, which will defeat blockbeat as we no longer guarantee the order channel arbitrator offers -> sweeper sweeps.
we could instead remove the advanceState in the ChannelArbitrator.Start since the channels will be handled in the main goroutine channelAttendant anyway.
fix it in the tapd side, which feels more appropriate as if the calls to methods of the AuxSweeper are blocking, we may have had some incorrect assumptions when using them in the sweeper.

contractcourt/chain_arbitrator.go

yyforyongyu

I tested out the second idea here, turns out it's a small change, and all the itests passed!

ziggie1984

Have some questions in terms of this new introduced behaviour, we are altering the lnd daemon logic slightly, which I think is ok and actually a better way to go instead of shutting down LND in case the startup of one arbitrator fails.

contractcourt/channel_arbitrator.go

ziggie1984 · 2024-12-03T14:53:05Z

contractcourt/channel_arbitrator.go

+	if err != nil {
+		log.Errorf("Unable to progress state machine after "+
+			"restart: %v", err)
+		return
+	}


This is a code change behaviour:

Previously we would not startup if the broadcast of the channel commitment failed, now we are just logging an error but we still continue running the daemon.

If we want to restore the behavior, we can use Criticalf here.

I kinda like this new approach, so if everybody is ok with it, I would favour not shutting down if one arbitrator fails

contractcourt/channel_arbitrator.go

Roasbeef · 2024-12-03T15:10:26Z

contractcourt/channel_arbitrator.go

+	if err != nil {
+		log.Errorf("Unable to progress state machine after "+
+			"restart: %v", err)
+		return
+	}


If we want to restore the behavior, we can use Criticalf here.

ziggie1984 · 2024-12-03T16:18:48Z

CI passed in the previous run, so I think this is gtg as soon as we have consensus whether we shutdown LND if a channel arbitrator fails to start or we just log an error and continue the process nonetheless.

yyforyongyu

LGTM🦾 Thanks for the quick fix!

contractcourt/channel_arbitrator.go

guggero

Nice, very clean solution, LGTM 🎉

contractcourt/channel_arbitrator.go

We decouple the state machine of the channel arbitrator from the start-up process so that we can startup the whole daemon reliably.

Roasbeef

LGTM 🦂

ziggie1984 force-pushed the non-blocking-startup-chan-arbitrator branch 2 times, most recently from 2f28012 to c1dc62b Compare November 30, 2024 10:10

ziggie1984 marked this pull request as ready for review November 30, 2024 10:11

ziggie1984 requested review from guggero and yyforyongyu November 30, 2024 10:11

guggero added this to the v0.18.4 milestone Dec 1, 2024

guggero added bug fix init Issues related to LND startup custom chans labels Dec 1, 2024

guggero reviewed Dec 2, 2024

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contractcourt/chain_arbitrator.go Outdated Show resolved Hide resolved

yyforyongyu requested changes Dec 2, 2024

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yyforyongyu reviewed Dec 2, 2024

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dstadulis assigned ffranr and ziggie1984 and unassigned ffranr Dec 3, 2024

ziggie1984 force-pushed the non-blocking-startup-chan-arbitrator branch from c1dc62b to 7efaffe Compare December 3, 2024 14:50

ziggie1984 commented Dec 3, 2024

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ziggie1984 requested review from guggero and yyforyongyu December 3, 2024 14:54

Roasbeef reviewed Dec 3, 2024

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ziggie1984 force-pushed the non-blocking-startup-chan-arbitrator branch 3 times, most recently from 514f29e to 2905de9 Compare December 3, 2024 16:16

yyforyongyu approved these changes Dec 3, 2024

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ziggie1984 force-pushed the non-blocking-startup-chan-arbitrator branch from 2905de9 to 8235f83 Compare December 3, 2024 21:14

guggero approved these changes Dec 4, 2024

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guggero requested a review from Roasbeef December 4, 2024 16:47

Roasbeef requested changes Dec 5, 2024

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ziggie1984 added 2 commits December 5, 2024 15:11

contractcourt: refactor start up of arbitrators

17bc882

We decouple the state machine of the channel arbitrator from the start-up process so that we can startup the whole daemon reliably.

docs: add release-notes

0004e31

ziggie1984 force-pushed the non-blocking-startup-chan-arbitrator branch from 8235f83 to 0004e31 Compare December 5, 2024 14:11

ziggie1984 requested a review from Roasbeef December 5, 2024 14:11

Roasbeef approved these changes Dec 5, 2024

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Roasbeef merged commit 8d7f085 into lightningnetwork:master Dec 5, 2024
27 of 34 checks passed

guggero mentioned this pull request Dec 5, 2024

release: create branch for v0.18.4-beta.rc2 #9335

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Don't block on channel arbitator startup #9324

Don't block on channel arbitator startup #9324

ziggie1984 commented Nov 29, 2024 •

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Don't block on channel arbitator startup #9324

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ziggie1984 commented Nov 29, 2024 •

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