core: bugfix state change race condition in txpool (#3412)

The transaction pool keeps track of the current nonce in its local pendingState. When a
new block comes in the pendingState is reset. During the reset it fetches multiple times
the current state through the use of the currentState callback. When a second block comes
in during the reset its possible that the state changes during the reset. If that block
holds transactions that are currently in the pool the local pendingState that is used to
determine nonces can get out of sync.

2 files changed, 124 insertions, 36 deletions

diff --git a/core/tx_pool.go b/core/tx_pool.go
index edcbc21eb..b805cf226 100644
--- a/core/tx_pool.go
+++ b/core/tx_pool.go
@@ -176,7 +176,7 @@ func (pool *TxPool) resetState() {
 	// any transactions that have been included in the block or
 	// have been invalidated because of another transaction (e.g.
 	// higher gas price)
-	pool.demoteUnexecutables()
+	pool.demoteUnexecutables(currentState)
 
 	// Update all accounts to the latest known pending nonce
 	for addr, list := range pool.pending {
@@ -185,7 +185,7 @@ func (pool *TxPool) resetState() {
 	}
 	// Check the queue and move transactions over to the pending if possible
 	// or remove those that have become invalid
-	pool.promoteExecutables()
+	pool.promoteExecutables(currentState)
 }
 
 func (pool *TxPool) Stop() {
@@ -196,8 +196,12 @@ func (pool *TxPool) Stop() {
 }
 
 func (pool *TxPool) State() *state.ManagedState {
-	pool.mu.RLock()
-	defer pool.mu.RUnlock()
+	pool.mu.Lock()
+	defer pool.mu.Unlock()
+
+	if pool.pendingState == nil {
+		pool.resetState()
+	}
 
 	return pool.pendingState
 }
@@ -237,21 +241,26 @@ func (pool *TxPool) Content() (map[common.Address]types.Transactions, map[common
 // Pending retrieves all currently processable transactions, groupped by origin
 // account and sorted by nonce. The returned transaction set is a copy and can be
 // freely modified by calling code.
-func (pool *TxPool) Pending() map[common.Address]types.Transactions {
+func (pool *TxPool) Pending() (map[common.Address]types.Transactions, error) {
 	pool.mu.Lock()
 	defer pool.mu.Unlock()
 
+	state, err := pool.currentState()
+	if err != nil {
+		return nil, err
+	}
+
 	// check queue first
-	pool.promoteExecutables()
+	pool.promoteExecutables(state)
 
 	// invalidate any txs
-	pool.demoteUnexecutables()
+	pool.demoteUnexecutables(state)
 
 	pending := make(map[common.Address]types.Transactions)
 	for addr, list := range pool.pending {
 		pending[addr] = list.Flatten()
 	}
-	return pending
+	return pending, nil
 }
 
 // SetLocal marks a transaction as local, skipping gas price
@@ -410,13 +419,19 @@ func (pool *TxPool) Add(tx *types.Transaction) error {
 	if err := pool.add(tx); err != nil {
 		return err
 	}
-	pool.promoteExecutables()
+
+	state, err := pool.currentState()
+	if err != nil {
+		return err
+	}
+
+	pool.promoteExecutables(state)
 
 	return nil
 }
 
 // AddBatch attempts to queue a batch of transactions.
-func (pool *TxPool) AddBatch(txs []*types.Transaction) {
+func (pool *TxPool) AddBatch(txs []*types.Transaction) error {
 	pool.mu.Lock()
 	defer pool.mu.Unlock()
 
@@ -425,7 +440,15 @@ func (pool *TxPool) AddBatch(txs []*types.Transaction) {
 			glog.V(logger.Debug).Infoln("tx error:", err)
 		}
 	}
-	pool.promoteExecutables()
+
+	state, err := pool.currentState()
+	if err != nil {
+		return err
+	}
+
+	pool.promoteExecutables(state)
+
+	return nil
 }
 
 // Get returns a transaction if it is contained in the pool
@@ -499,17 +522,7 @@ func (pool *TxPool) removeTx(hash common.Hash) {
 // promoteExecutables moves transactions that have become processable from the
 // future queue to the set of pending transactions. During this process, all
 // invalidated transactions (low nonce, low balance) are deleted.
-func (pool *TxPool) promoteExecutables() {
-	// Init delayed since tx pool could have been started before any state sync
-	if pool.pendingState == nil {
-		pool.resetState()
-	}
-	// Retrieve the current state to allow nonce and balance checking
-	state, err := pool.currentState()
-	if err != nil {
-		glog.Errorf("Could not get current state: %v", err)
-		return
-	}
+func (pool *TxPool) promoteExecutables(state *state.StateDB) {
 	// Iterate over all accounts and promote any executable transactions
 	queued := uint64(0)
 	for addr, list := range pool.queue {
@@ -645,13 +658,7 @@ func (pool *TxPool) promoteExecutables() {
 // demoteUnexecutables removes invalid and processed transactions from the pools
 // executable/pending queue and any subsequent transactions that become unexecutable
 // are moved back into the future queue.
-func (pool *TxPool) demoteUnexecutables() {
-	// Retrieve the current state to allow nonce and balance checking
-	state, err := pool.currentState()
-	if err != nil {
-		glog.V(logger.Info).Infoln("failed to get current state: %v", err)
-		return
-	}
+func (pool *TxPool) demoteUnexecutables(state *state.StateDB) {
 	// Iterate over all accounts and demote any non-executable transactions
 	for addr, list := range pool.pending {
 		nonce := state.GetNonce(addr)
diff --git a/core/tx_pool_test.go b/core/tx_pool_test.go
index 009d19886..3e516735b 100644
--- a/core/tx_pool_test.go
+++ b/core/tx_pool_test.go
@@ -51,6 +51,80 @@ func deriveSender(tx *types.Transaction) (common.Address, error) {
 	return types.Sender(types.HomesteadSigner{}, tx)
 }
 
+// This test simulates a scenario where a new block is imported during a
+// state reset and tests whether the pending state is in sync with the
+// block head event that initiated the resetState().
+func TestStateChangeDuringPoolReset(t *testing.T) {
+	var (
+		db, _      = ethdb.NewMemDatabase()
+		key, _     = crypto.GenerateKey()
+		address    = crypto.PubkeyToAddress(key.PublicKey)
+		mux        = new(event.TypeMux)
+		statedb, _ = state.New(common.Hash{}, db)
+		trigger    = false
+	)
+
+	// setup pool with 2 transaction in it
+	statedb.SetBalance(address, new(big.Int).Mul(common.Big1, common.Ether))
+
+	tx0 := transaction(0, big.NewInt(100000), key)
+	tx1 := transaction(1, big.NewInt(100000), key)
+
+	// stateFunc is used multiple times to reset the pending state.
+	// when simulate is true it will create a state that indicates
+	// that tx0 and tx1 are included in the chain.
+	stateFunc := func() (*state.StateDB, error) {
+		// delay "state change" by one. The tx pool fetches the
+		// state multiple times and by delaying it a bit we simulate
+		// a state change between those fetches.
+		stdb := statedb
+		if trigger {
+			statedb, _ = state.New(common.Hash{}, db)
+			// simulate that the new head block included tx0 and tx1
+			statedb.SetNonce(address, 2)
+			statedb.SetBalance(address, new(big.Int).Mul(common.Big1, common.Ether))
+			trigger = false
+		}
+		return stdb, nil
+	}
+
+	gasLimitFunc := func() *big.Int { return big.NewInt(1000000000) }
+
+	txpool := NewTxPool(testChainConfig(), mux, stateFunc, gasLimitFunc)
+	txpool.resetState()
+
+	nonce := txpool.State().GetNonce(address)
+	if nonce != 0 {
+		t.Fatalf("Invalid nonce, want 0, got %d", nonce)
+	}
+
+	txpool.AddBatch(types.Transactions{tx0, tx1})
+
+	nonce = txpool.State().GetNonce(address)
+	if nonce != 2 {
+		t.Fatalf("Invalid nonce, want 2, got %d", nonce)
+	}
+
+	// trigger state change in the background
+	trigger = true
+
+	txpool.resetState()
+
+	pendingTx, err := txpool.Pending()
+	if err != nil {
+		t.Fatalf("Could not fetch pending transactions: %v", err)
+	}
+
+	for addr, txs := range pendingTx {
+		t.Logf("%0x: %d\n", addr, len(txs))
+	}
+
+	nonce = txpool.State().GetNonce(address)
+	if nonce != 2 {
+		t.Fatalf("Invalid nonce, want 2, got %d", nonce)
+	}
+}
+
 func TestInvalidTransactions(t *testing.T) {
 	pool, key := setupTxPool()
 
@@ -97,9 +171,10 @@ func TestTransactionQueue(t *testing.T) {
 	from, _ := deriveSender(tx)
 	currentState, _ := pool.currentState()
 	currentState.AddBalance(from, big.NewInt(1000))
+	pool.resetState()
 	pool.enqueueTx(tx.Hash(), tx)
 
-	pool.promoteExecutables()
+	pool.promoteExecutables(currentState)
 	if len(pool.pending) != 1 {
 		t.Error("expected valid txs to be 1 is", len(pool.pending))
 	}
@@ -108,7 +183,7 @@ func TestTransactionQueue(t *testing.T) {
 	from, _ = deriveSender(tx)
 	currentState.SetNonce(from, 2)
 	pool.enqueueTx(tx.Hash(), tx)
-	pool.promoteExecutables()
+	pool.promoteExecutables(currentState)
 	if _, ok := pool.pending[from].txs.items[tx.Nonce()]; ok {
 		t.Error("expected transaction to be in tx pool")
 	}
@@ -124,11 +199,13 @@ func TestTransactionQueue(t *testing.T) {
 	from, _ = deriveSender(tx1)
 	currentState, _ = pool.currentState()
 	currentState.AddBalance(from, big.NewInt(1000))
+	pool.resetState()
+
 	pool.enqueueTx(tx1.Hash(), tx1)
 	pool.enqueueTx(tx2.Hash(), tx2)
 	pool.enqueueTx(tx3.Hash(), tx3)
 
-	pool.promoteExecutables()
+	pool.promoteExecutables(currentState)
 
 	if len(pool.pending) != 1 {
 		t.Error("expected tx pool to be 1, got", len(pool.pending))
@@ -225,7 +302,8 @@ func TestTransactionDoubleNonce(t *testing.T) {
 	if err := pool.add(tx2); err != nil {
 		t.Error("didn't expect error", err)
 	}
-	pool.promoteExecutables()
+	state, _ := pool.currentState()
+	pool.promoteExecutables(state)
 	if pool.pending[addr].Len() != 1 {
 		t.Error("expected 1 pending transactions, got", pool.pending[addr].Len())
 	}
@@ -236,7 +314,7 @@ func TestTransactionDoubleNonce(t *testing.T) {
 	if err := pool.add(tx3); err != nil {
 		t.Error("didn't expect error", err)
 	}
-	pool.promoteExecutables()
+	pool.promoteExecutables(state)
 	if pool.pending[addr].Len() != 1 {
 		t.Error("expected 1 pending transactions, got", pool.pending[addr].Len())
 	}
@@ -295,6 +373,7 @@ func TestRemovedTxEvent(t *testing.T) {
 	from, _ := deriveSender(tx)
 	currentState, _ := pool.currentState()
 	currentState.AddBalance(from, big.NewInt(1000000000000))
+	pool.resetState()
 	pool.eventMux.Post(RemovedTransactionEvent{types.Transactions{tx}})
 	pool.eventMux.Post(ChainHeadEvent{nil})
 	if pool.pending[from].Len() != 1 {
@@ -452,6 +531,7 @@ func TestTransactionQueueAccountLimiting(t *testing.T) {
 
 	state, _ := pool.currentState()
 	state.AddBalance(account, big.NewInt(1000000))
+	pool.resetState()
 
 	// Keep queuing up transactions and make sure all above a limit are dropped
 	for i := uint64(1); i <= maxQueuedPerAccount+5; i++ {
@@ -564,6 +644,7 @@ func TestTransactionPendingLimiting(t *testing.T) {
 
 	state, _ := pool.currentState()
 	state.AddBalance(account, big.NewInt(1000000))
+	pool.resetState()
 
 	// Keep queuing up transactions and make sure all above a limit are dropped
 	for i := uint64(0); i < maxQueuedPerAccount+5; i++ {
@@ -733,7 +814,7 @@ func benchmarkPendingDemotion(b *testing.B, size int) {
 	// Benchmark the speed of pool validation
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		pool.demoteUnexecutables()
+		pool.demoteUnexecutables(state)
 	}
 }
 
@@ -757,7 +838,7 @@ func benchmarkFuturePromotion(b *testing.B, size int) {
 	// Benchmark the speed of pool validation
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		pool.promoteExecutables()
+		pool.promoteExecutables(state)
 	}
 }