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[v0.20.x-branch] Backport #10540: discovery: fix gossiper shutdown deadlock #10554

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yyforyongyu merged 2 commits into from
Feb 6, 2026
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[v0.20.x-branch] Backport #10540: discovery: fix gossiper shutdown deadlock #10554

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81d4da7
discovery: fix gossiper shutdown deadlock
morehouse Feb 2, 2026
f427fee
docs: add release note for #10540
morehouse Feb 3, 2026
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9 changes: 8 additions & 1 deletion discovery/gossiper.go
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Original file line number Diff line number Diff line change
Expand Up @@ -876,7 +876,14 @@ func (d *AuthenticatedGossiper) stop() {
func (d *AuthenticatedGossiper) ProcessRemoteAnnouncement(ctx context.Context,
msg lnwire.Message, peer lnpeer.Peer) chan error {

errChan := make(chan error, 1)
// Buffer up to two messages on errChan since up to two messages may be
// written and not all callers of this function actually read from
// errChan. Without this buffer goroutines end up blocking on writes to
// errChan, which prevents the gossiper from shutting down cleanly.
//
// TODO(ziggie): Redesign this once the actor model pattern becomes
// available. See https://github.com/lightningnetwork/lnd/pull/9820.
errChan := make(chan error, 2)

// For messages in the known set of channel series queries, we'll
// dispatch the message directly to the GossipSyncer, and skip the main
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61 changes: 61 additions & 0 deletions discovery/gossiper_test.go
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Expand Up @@ -5235,3 +5235,64 @@ func TestRecoverGossipPanicNilJobID(t *testing.T) {
t.Fatal("timeout waiting for error")
}
}

// TestGossiperShutdownWrongChainAnnouncement tests that the gossiper can shut
// down cleanly after processing a channel announcement with the wrong chain
// hash. This is a regression test for a bug where the gossiper would deadlock
// on shutdown because more errors were sent on the error channel than it would
// buffer, and no one was reading those error messages.
//
// In this test we trigger the sending of two error messages:
// 1. First send when rejecting the wrong-chain announcement
// 2. Second send when SignalDependents returns an error
//
// Since the error channel had a buffer of 1, the second send would block
// forever, preventing the goroutine from completing and causing Stop() to hang
// on wg.Wait().
func TestGossiperShutdownWrongChainAnnouncement(t *testing.T) {
t.Parallel()

// Create a test context with the gossiper configured for MainNet.
tCtx, err := createTestCtx(t, 0, false)
require.NoError(t, err)

// Create a channel announcement with:
// 1. Wrong chain hash (SimNet instead of MainNet)
// 2. NodeID1 == NodeID2
//
// The first condition triggers the first error message to be sent, and
// the second condition causes SignalDependents to attempt to remove the
// same dependent job twice, which then triggers the second error
// message to be sent.
wrongChainAnn := &lnwire.ChannelAnnouncement1{
ChainHash: *chaincfg.SimNetParams.GenesisHash,
ShortChannelID: lnwire.ShortChannelID{
BlockHeight: 1,
TxIndex: 0,
TxPosition: 0,
},
Features: testFeatures,
}
// Use the SAME public key for NodeID1 and NodeID2 to trigger the
// second error message.
copy(wrongChainAnn.NodeID1[:], remoteKeyPub1.SerializeCompressed())
copy(wrongChainAnn.NodeID2[:], remoteKeyPub1.SerializeCompressed())
copy(wrongChainAnn.BitcoinKey1[:], bitcoinKeyPub1.SerializeCompressed())
copy(wrongChainAnn.BitcoinKey2[:], bitcoinKeyPub2.SerializeCompressed())

nodePeer := &mockPeer{remoteKeyPub1, nil, nil, atomic.Bool{}}

// Process the announcement without reading from the error channel,
// exactly as Brontide does.
_ = tCtx.gossiper.ProcessRemoteAnnouncement(
t.Context(), wrongChainAnn, nodePeer,
)

// Give the gossiper time to process the announcement.
time.Sleep(100 * time.Millisecond)

// Now stop the gossiper. This should complete without hanging.
// If the bug is present, Stop() will hang forever because a goroutine
// is blocked trying to send to the error channel a second time.
require.NoError(t, tCtx.gossiper.Stop())
}
7 changes: 7 additions & 0 deletions docs/release-notes/release-notes-0.20.1.md
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Expand Up @@ -82,6 +82,12 @@
The fix adds automatic format detection to handle both legacy (raw feature
bits) and new (length-prefixed) formats.

* [Fixed a shutdown
deadlock](https://github.com/lightningnetwork/lnd/pull/10540) in the gossiper.
Certain gossip messages could cause multiple error messages to be sent on a
channel that was only expected to be used for a single message. The erring
goroutine would block on the second send, leading to a deadlock at shutdown.

# New Features

## Functional Enhancements
Expand Down Expand Up @@ -152,4 +158,5 @@

* Abdulkbk
* bitromortac
* Matt Morehouse
* Ziggie
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