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[bug]: ChannelArbitrator does not cleanly stop #8149

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Crypt-iQ opened this issue Nov 3, 2023 · 1 comment · Fixed by #9253 · May be fixed by #9264
Open

[bug]: ChannelArbitrator does not cleanly stop #8149

Crypt-iQ opened this issue Nov 3, 2023 · 1 comment · Fixed by #9253 · May be fixed by #9264
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bug Unintended code behaviour P3 might get fixed, nice to have

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@Crypt-iQ
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Crypt-iQ commented Nov 3, 2023

When a ChannelArbitrator is finished with its duties, it attempts to stop itself but can't:

The channelAttendant goroutine calls advanceState which calls stateStep which hits this line if the state is StateFullyResolved:

lnd/contractcourt/channel_arbitrator.go

Lines 1280 to 1283 in e6fbaaf

if err := c.cfg.MarkChannelResolved(); err != nil {
log.Errorf("unable to mark channel resolved: %v", err)
return StateError, closeTx, err
}

MarkChannelResolved calls ResolveContract:

lnd/contractcourt/chain_arbitrator.go

Lines 399 to 404 in e6fbaaf

arbCfg.MarkChannelResolved = func() error {
if c.cfg.NotifyFullyResolvedChannel != nil {
c.cfg.NotifyFullyResolvedChannel(chanPoint)
}
return c.ResolveContract(chanPoint)

ResolveContract calls Stop on the ChannelArbitrator:

lnd/contractcourt/chain_arbitrator.go

Lines 465 to 471 in e6fbaaf

if chainArb != nil {
arbLog = chainArb.log
if err := chainArb.Stop(); err != nil {
log.Warnf("unable to stop ChannelArbitrator(%v): %v",
chanPoint, err)
}

This will close the quit channel and wait for the waitgroup counter to go to zero. However, because this can be called from channelAttendant, the goroutine is waiting for itself to be cleaned up and will just hang. This doesn't cause the node to be unresponsive, but the ChannelArbitrator will sit there and not properly stop.

h/t @bitromortac
@Crypt-iQ Crypt-iQ added the bug Unintended code behaviour label Nov 3, 2023
@saubyk saubyk added P2 should be fixed if one has time P3 might get fixed, nice to have and removed P2 should be fixed if one has time labels Nov 8, 2023
This was referenced Nov 9, 2024
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@ziggie1984
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The fix is actually in 9253, so reopening.

@ziggie1984 ziggie1984 reopened this Nov 20, 2024
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fix chanArb deadlock ziggie1984/lnd
Fix channel arbitrator lingering goroutine ziggie1984/lnd
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@Crypt-iQ @saubyk @ziggie1984