Forkchoice: expose if no tip is viable (#11153)

* Forkchoice: expose if no tip is viable

This PR changes the behavior on when the node is considered optimistic.
A call to `blockchain.IsOptimistic()` relies solely on forkchoice, if
all tips are invalid, then it's optimistic. If the current headroot is
not in forkchoice then it's optimistic.

A call to `blockchain.IsOptimisticForRoot()` will return true if the
requested root is headroot and it's not found in forkchoice

* update comment

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

beacon-chain/blockchain/chain_info.go

@@ -307,7 +307,19 @@ func (s *Service) IsOptimistic(ctx context.Context) (bool, error) {
 	headRoot := s.head.root
 	s.headLock.RUnlock()
 
-	return s.IsOptimisticForRoot(ctx, headRoot)
+	if s.cfg.ForkChoiceStore.AllTipsAreInvalid() {
+		return true, nil
+	}
+	optimistic, err := s.cfg.ForkChoiceStore.IsOptimistic(headRoot)
+	if err == nil {
+		return optimistic, nil
+	}
+	if err != protoarray.ErrUnknownNodeRoot && err != doublylinkedtree.ErrNilNode {
+		return true, err
+	}
+	// If fockchoice does not have the headroot, then the node is considered
+	// optimistic
+	return true, nil
 }
 
 // IsFinalized returns true if the input root is finalized.
@@ -329,24 +341,24 @@ func (s *Service) IsOptimisticForRoot(ctx context.Context, root [32]byte) (bool,
 	if err != protoarray.ErrUnknownNodeRoot && err != doublylinkedtree.ErrNilNode {
 		return false, err
 	}
+	// if the requested root is the headroot and the root is not found in
+	// forkchoice, the node should respond that it is optimistic
+	headRoot, err := s.HeadRoot(ctx)
+	if err != nil {
+		return true, err
+	}
+	if bytes.Equal(headRoot, root[:]) {
+		return true, nil
+	}
+
 	ss, err := s.cfg.BeaconDB.StateSummary(ctx, root)
 	if err != nil {
 		return false, err
 	}
+
 	if ss == nil {
-		// if the requested root is the headroot we should treat the
-		// node as optimistic. This can happen if we pruned INVALID
-		// nodes and no viable head is available.
-		headRoot, err := s.HeadRoot(ctx)
-		if err != nil {
-			return true, err
-		}
-		if bytes.Equal(headRoot, root[:]) {
-			return true, nil
-		}
 		return true, errInvalidNilSummary
 	}
-
 	validatedCheckpoint, err := s.cfg.BeaconDB.LastValidatedCheckpoint(ctx)
 	if err != nil {
 		return false, err

beacon-chain/blockchain/process_block_test.go

@@ -3002,10 +3002,12 @@ func TestStore_NoViableHead_Reboot_DoublyLinkedTree(t *testing.T) {
 	headRoot, err := service.HeadRoot(ctx)
 	require.NoError(t, err)
 	require.Equal(t, genesisRoot, bytesutil.ToBytes32(headRoot))
-	// The node is not optimistic now
+	// The node is not optimistic now until the first call to forkchoice
+	// Head()
 	optimistic, err := service.IsOptimistic(ctx)
 	require.NoError(t, err)
 	require.Equal(t, false, optimistic)
+	require.Equal(t, false, service.ForkChoicer().AllTipsAreInvalid())
 
 	// Check that the node's justified checkpoint does not agree with the
 	// last valid state's justified checkpoint
@@ -3031,7 +3033,8 @@ func TestStore_NoViableHead_Reboot_DoublyLinkedTree(t *testing.T) {
 
 	optimistic, err = service.IsOptimistic(ctx)
 	require.NoError(t, err)
-	require.Equal(t, false, optimistic)
+	require.Equal(t, true, optimistic)
+	require.Equal(t, true, service.ForkChoicer().AllTipsAreInvalid())
 	st, err = service.cfg.StateGen.StateByRoot(ctx, root)
 	require.NoError(t, err)
 	// Import blocks 21--30 (Epoch 3 was not enough to justify 2)
@@ -3057,7 +3060,233 @@ func TestStore_NoViableHead_Reboot_DoublyLinkedTree(t *testing.T) {
 
 	optimistic, err = service.IsOptimistic(ctx)
 	require.NoError(t, err)
+	require.Equal(t, true, optimistic)
+	require.Equal(t, true, service.ForkChoicer().AllTipsAreInvalid())
+
+	// Import block 30, it should justify Epoch 4 and become HEAD, the node
+	// recovers
+	driftGenesisTime(service, 30, 0)
+	b, err = util.GenerateFullBlockBellatrix(st, keys, util.DefaultBlockGenConfig(), 30)
+	require.NoError(t, err)
+	wsb, err = consensusblocks.NewSignedBeaconBlock(b)
+	require.NoError(t, err)
+	root, err = b.Block.HashTreeRoot()
+	require.NoError(t, err)
+	err = service.onBlock(ctx, wsb, root)
+	require.NoError(t, err)
+	require.Equal(t, root, service.ForkChoicer().CachedHeadRoot())
+	headRoot, err = service.HeadRoot(ctx)
+	require.NoError(t, err)
+	require.Equal(t, root, bytesutil.ToBytes32(headRoot))
+
+	sjc = service.CurrentJustifiedCheckpt()
+	require.Equal(t, types.Epoch(4), sjc.Epoch)
+	optimistic, err = service.IsOptimistic(ctx)
+	require.NoError(t, err)
+	require.Equal(t, false, optimistic)
+	require.Equal(t, false, service.ForkChoicer().AllTipsAreInvalid())
+}
+
+// See the description in #10777 and #10782 for the full setup
+// We sync optimistically a chain of blocks. Block 12 is the first block in Epoch
+// 2 (and the merge block in this sequence). Block 18 justifies it and Block 19 returns
+// INVALID from NewPayload, with LVH block 12. No head is viable. We check that
+// the node can reboot from this state
+func TestStore_NoViableHead_Reboot_Protoarray(t *testing.T) {
+	params.SetupTestConfigCleanup(t)
+	config := params.BeaconConfig()
+	config.SlotsPerEpoch = 6
+	config.AltairForkEpoch = 1
+	config.BellatrixForkEpoch = 2
+	config.SafeSlotsToImportOptimistically = 0
+	params.OverrideBeaconConfig(config)
+
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+
+	mockEngine := &mockExecution.EngineClient{ErrNewPayload: execution.ErrAcceptedSyncingPayloadStatus, ErrForkchoiceUpdated: execution.ErrAcceptedSyncingPayloadStatus}
+	attSrv, err := attestations.NewService(ctx, &attestations.Config{})
+	require.NoError(t, err)
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithAttestationPool(attestations.NewPool()),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(protoarray.New()),
+		WithStateNotifier(&mock.MockStateNotifier{}),
+		WithExecutionEngineCaller(mockEngine),
+		WithProposerIdsCache(cache.NewProposerPayloadIDsCache()),
+		WithAttestationService(attSrv),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	genesisState, keys := util.DeterministicGenesisState(t, 64)
+	stateRoot, err := genesisState.HashTreeRoot(ctx)
+	require.NoError(t, err, "Could not hash genesis state")
+	genesis := blocks.NewGenesisBlock(stateRoot[:])
+	wsb, err := consensusblocks.NewSignedBeaconBlock(genesis)
+	require.NoError(t, err)
+	genesisRoot, err := genesis.Block.HashTreeRoot()
+	require.NoError(t, err, "Could not get signing root")
+	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wsb), "Could not save genesis block")
+	require.NoError(t, service.saveGenesisData(ctx, genesisState))
+
+	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, genesisState, genesisRoot), "Could not save genesis state")
+	require.NoError(t, service.cfg.BeaconDB.SaveHeadBlockRoot(ctx, genesisRoot), "Could not save genesis state")
+
+	for i := 1; i < 6; i++ {
+		driftGenesisTime(service, int64(i), 0)
+		st, err := service.HeadState(ctx)
+		require.NoError(t, err)
+		b, err := util.GenerateFullBlock(st, keys, util.DefaultBlockGenConfig(), types.Slot(i))
+		require.NoError(t, err)
+		wsb, err := consensusblocks.NewSignedBeaconBlock(b)
+		require.NoError(t, err)
+		root, err := b.Block.HashTreeRoot()
+		require.NoError(t, err)
+		require.NoError(t, service.onBlock(ctx, wsb, root))
+	}
+
+	for i := 6; i < 12; i++ {
+		driftGenesisTime(service, int64(i), 0)
+		st, err := service.HeadState(ctx)
+		require.NoError(t, err)
+		b, err := util.GenerateFullBlockAltair(st, keys, util.DefaultBlockGenConfig(), types.Slot(i))
+		require.NoError(t, err)
+		wsb, err := consensusblocks.NewSignedBeaconBlock(b)
+		require.NoError(t, err)
+		root, err := b.Block.HashTreeRoot()
+		require.NoError(t, err)
+		err = service.onBlock(ctx, wsb, root)
+		require.NoError(t, err)
+	}
+
+	// import the merge block
+	driftGenesisTime(service, 12, 0)
+	st, err := service.HeadState(ctx)
+	require.NoError(t, err)
+	b, err := util.GenerateFullBlockBellatrix(st, keys, util.DefaultBlockGenConfig(), 12)
+	require.NoError(t, err)
+	wsb, err = consensusblocks.NewSignedBeaconBlock(b)
+	require.NoError(t, err)
+	lastValidRoot, err := b.Block.HashTreeRoot()
+	require.NoError(t, err)
+	err = service.onBlock(ctx, wsb, lastValidRoot)
+	require.NoError(t, err)
+	// save the post state and the payload Hash of this block since it will
+	// be the LVH
+	validHeadState, err := service.HeadState(ctx)
+	require.NoError(t, err)
+	lvh := b.Block.Body.ExecutionPayload.BlockHash
+	validjc := validHeadState.CurrentJustifiedCheckpoint()
+	require.Equal(t, types.Epoch(0), validjc.Epoch)
+
+	// import blocks 13 through 18 to justify 12
+	for i := 13; i < 19; i++ {
+		driftGenesisTime(service, int64(i), 0)
+		st, err := service.HeadState(ctx)
+		require.NoError(t, err)
+		b, err := util.GenerateFullBlockBellatrix(st, keys, util.DefaultBlockGenConfig(), types.Slot(i))
+		require.NoError(t, err)
+		wsb, err := consensusblocks.NewSignedBeaconBlock(b)
+		require.NoError(t, err)
+		root, err := b.Block.HashTreeRoot()
+		require.NoError(t, err)
+		require.NoError(t, service.onBlock(ctx, wsb, root))
+	}
+	// Check that we have justified the second epoch
+	jc := service.ForkChoicer().JustifiedCheckpoint()
+	require.Equal(t, types.Epoch(2), jc.Epoch)
+
+	// import block 19 to find out that the whole chain 13--18 was in fact
+	// invalid
+	mockEngine = &mockExecution.EngineClient{ErrNewPayload: execution.ErrInvalidPayloadStatus, NewPayloadResp: lvh}
+	service.cfg.ExecutionEngineCaller = mockEngine
+	driftGenesisTime(service, 19, 0)
+	st, err = service.HeadState(ctx)
+	require.NoError(t, err)
+	b, err = util.GenerateFullBlockBellatrix(st, keys, util.DefaultBlockGenConfig(), 19)
+	require.NoError(t, err)
+	wsb, err = consensusblocks.NewSignedBeaconBlock(b)
+	require.NoError(t, err)
+	root, err := b.Block.HashTreeRoot()
+	require.NoError(t, err)
+	err = service.onBlock(ctx, wsb, root)
+	require.ErrorContains(t, "received an INVALID payload from execution engine", err)
+
+	// Check that the headroot/state are not in DB and restart the node
+	blk, err := service.cfg.BeaconDB.HeadBlock(ctx)
+	require.NoError(t, err) // HeadBlock returns no error when headroot == nil
+	require.Equal(t, blk, nil)
+
+	require.NoError(t, service.StartFromSavedState(genesisState))
+
+	// Forkchoice does not have a cached headroot now
+	require.Equal(t, [32]byte{}, service.ForkChoicer().CachedHeadRoot())
+	// Service's store has the finalized state as headRoot
+	headRoot, err := service.HeadRoot(ctx)
+	require.NoError(t, err)
+	require.Equal(t, genesisRoot, bytesutil.ToBytes32(headRoot))
+	// The node is not optimistic now until the first call to forkchoice
+	// Head()
+	optimistic, err := service.IsOptimistic(ctx)
+	require.NoError(t, err)
 	require.Equal(t, false, optimistic)
+	require.Equal(t, false, service.ForkChoicer().AllTipsAreInvalid())
+
+	// Check that the node's justified checkpoint does not agree with the
+	// last valid state's justified checkpoint
+	sjc := service.CurrentJustifiedCheckpt()
+	require.Equal(t, types.Epoch(2), sjc.Epoch)
+
+	// import another block based on the last valid head state
+	mockEngine = &mockExecution.EngineClient{}
+	service.cfg.ExecutionEngineCaller = mockEngine
+	driftGenesisTime(service, 20, 0)
+	b, err = util.GenerateFullBlockBellatrix(validHeadState, keys, &util.BlockGenConfig{}, 20)
+	require.NoError(t, err)
+	wsb, err = consensusblocks.NewSignedBeaconBlock(b)
+	require.NoError(t, err)
+	root, err = b.Block.HashTreeRoot()
+	require.NoError(t, err)
+	require.NoError(t, service.onBlock(ctx, wsb, root))
+	// Check that the head is still INVALID and the node is not optimistic
+	require.Equal(t, [32]byte{}, service.ForkChoicer().CachedHeadRoot())
+	headRoot, err = service.HeadRoot(ctx)
+	require.NoError(t, err)
+	require.Equal(t, genesisRoot, bytesutil.ToBytes32(headRoot))
+
+	optimistic, err = service.IsOptimistic(ctx)
+	require.NoError(t, err)
+	require.Equal(t, true, optimistic)
+	require.Equal(t, true, service.ForkChoicer().AllTipsAreInvalid())
+	st, err = service.cfg.StateGen.StateByRoot(ctx, root)
+	require.NoError(t, err)
+	// Import blocks 21--30 (Epoch 3 was not enough to justify 2)
+	for i := 21; i < 30; i++ {
+		driftGenesisTime(service, int64(i), 0)
+		require.NoError(t, err)
+		b, err := util.GenerateFullBlockBellatrix(st, keys, util.DefaultBlockGenConfig(), types.Slot(i))
+		require.NoError(t, err)
+		wsb, err := consensusblocks.NewSignedBeaconBlock(b)
+		require.NoError(t, err)
+		root, err := b.Block.HashTreeRoot()
+		require.NoError(t, err)
+		err = service.onBlock(ctx, wsb, root)
+		require.NoError(t, err)
+		st, err = service.cfg.StateGen.StateByRoot(ctx, root)
+		require.NoError(t, err)
+	}
+	// Head should still be INVALID and the node is not optimistic
+	require.Equal(t, [32]byte{}, service.ForkChoicer().CachedHeadRoot())
+	headRoot, err = service.HeadRoot(ctx)
+	require.NoError(t, err)
+	require.Equal(t, genesisRoot, bytesutil.ToBytes32(headRoot))
+
+	optimistic, err = service.IsOptimistic(ctx)
+	require.NoError(t, err)
+	require.Equal(t, true, optimistic)
+	require.Equal(t, true, service.ForkChoicer().AllTipsAreInvalid())
 
 	// Import block 30, it should justify Epoch 4 and become HEAD, the node
 	// recovers
@@ -3080,6 +3309,7 @@ func TestStore_NoViableHead_Reboot_DoublyLinkedTree(t *testing.T) {
 	optimistic, err = service.IsOptimistic(ctx)
 	require.NoError(t, err)
 	require.Equal(t, false, optimistic)
+	require.Equal(t, false, service.ForkChoicer().AllTipsAreInvalid())
 }
 
 // Helper function to simulate the block being on time or delayed for proposer

beacon-chain/forkchoice/doubly-linked-tree/optimistic_sync.go

@@ -109,3 +109,10 @@ func (s *Store) removeNodeAndChildren(ctx context.Context, node *Node, invalidRo
 	delete(s.nodeByPayload, node.payloadHash)
 	return invalidRoots, nil
 }
+
+// AllTipsAreInvalid returns true if no forkchoice tip is viable for head
+func (f *ForkChoice) AllTipsAreInvalid() bool {
+	f.store.nodesLock.RLock()
+	defer f.store.nodesLock.RUnlock()
+	return f.store.allTipsAreInvalid
+}

beacon-chain/forkchoice/doubly-linked-tree/store.go

@@ -93,9 +93,11 @@ func (s *Store) head(ctx context.Context) ([32]byte, error) {
 	}
 
 	if !bestDescendant.viableForHead(s.justifiedCheckpoint.Epoch, s.finalizedCheckpoint.Epoch) {
+		s.allTipsAreInvalid = true
 		return [32]byte{}, fmt.Errorf("head at slot %d with weight %d is not eligible, finalizedEpoch, justified Epoch %d, %d != %d, %d",
 			bestDescendant.slot, bestDescendant.weight/10e9, bestDescendant.finalizedEpoch, bestDescendant.justifiedEpoch, s.finalizedCheckpoint.Epoch, s.justifiedCheckpoint.Epoch)
 	}
+	s.allTipsAreInvalid = false
 
 	// Update metrics.
 	if bestDescendant != s.headNode {

beacon-chain/forkchoice/doubly-linked-tree/types.go

@@ -38,6 +38,7 @@ type Store struct {
 	proposerBoostLock             sync.RWMutex
 	checkpointsLock               sync.RWMutex
 	genesisTime                   uint64
+	allTipsAreInvalid             bool // tracks if all tips are not viable for head
 }
 
 // Node defines the individual block which includes its block parent, ancestor and how much weight accounted for it.

beacon-chain/forkchoice/interfaces.go

@@ -26,6 +26,7 @@ type HeadRetriever interface {
 	CachedHeadRoot() [32]byte
 	Tips() ([][32]byte, []types.Slot)
 	IsOptimistic(root [32]byte) (bool, error)
+	AllTipsAreInvalid() bool
 }
 
 // BlockProcessor processes the block that's used for accounting fork choice.

beacon-chain/forkchoice/protoarray/optimistic_sync.go

@@ -171,3 +171,10 @@ func (f *ForkChoice) SetOptimisticToInvalid(ctx context.Context, root, parentRoo
 	}
 	return invalidRoots, nil
 }
+
+// AllTipsAreInvalid returns true if no forkchoice tip is viable for head
+func (f *ForkChoice) AllTipsAreInvalid() bool {
+	f.store.nodesLock.RLock()
+	defer f.store.nodesLock.RUnlock()
+	return f.store.allTipsAreInvalid
+}

beacon-chain/forkchoice/protoarray/store.go

@@ -402,9 +402,11 @@ func (s *Store) head(ctx context.Context) ([32]byte, error) {
 	bestNode := s.nodes[bestDescendantIndex]
 
 	if !s.viableForHead(bestNode) {
+		s.allTipsAreInvalid = true
 		return [32]byte{}, fmt.Errorf("head at slot %d with weight %d is not eligible, finalizedEpoch %d != %d, justifiedEpoch %d != %d",
 			bestNode.slot, bestNode.weight/10e9, bestNode.finalizedEpoch, s.finalizedCheckpoint.Epoch, bestNode.justifiedEpoch, s.justifiedCheckpoint.Epoch)
 	}
+	s.allTipsAreInvalid = false
 
 	// Update metrics and tracked head Root
 	if bestNode.root != s.lastHeadRoot {

beacon-chain/forkchoice/protoarray/types.go

@@ -39,6 +39,7 @@ type Store struct {
 	proposerBoostLock             sync.RWMutex
 	checkpointsLock               sync.RWMutex
 	genesisTime                   uint64
+	allTipsAreInvalid             bool // tracks if all tips are not viable for head
 }
 
 // Node defines the individual block which includes its block parent, ancestor and how much weight accounted for it.