core: fix sync reset in pruned nodes (#31638)

This is an attempt at fixing #31601. I think what happens is the startup
logic will try to get the full block body (it's `bc.loadLastState`) and
fail because genesis block has been pruned from the freezer. This will
cause it to keep repeating the reset logic, causing a deadlock.

This can happen when due to an unsuccessful sync we don't have the state
for the head (or any other state) fully, and try to redo the snap sync.

---------

Co-authored-by: Gary Rong <garyrong0905@gmail.com>

core/blockchain.go

@@ -514,19 +514,33 @@ func (bc *BlockChain) loadLastState() error {
 		log.Warn("Empty database, resetting chain")
 		return bc.Reset()
 	}
-	// Make sure the entire head block is available
-	headBlock := bc.GetBlockByHash(head)
+	headHeader := bc.GetHeaderByHash(head)
+	if headHeader == nil {
+		// Corrupt or empty database, init from scratch
+		log.Warn("Head header missing, resetting chain", "hash", head)
+		return bc.Reset()
+	}
+
+	var headBlock *types.Block
+	if cmp := headHeader.Number.Cmp(new(big.Int)); cmp == 1 {
+		// Make sure the entire head block is available.
+		headBlock = bc.GetBlockByHash(head)
+	} else if cmp == 0 {
+		// On a pruned node the block body might not be available. But a pruned
+		// block should never be the head block. The only exception is when, as
+		// a last resort, chain is reset to genesis.
+		headBlock = bc.genesisBlock
+	}
 	if headBlock == nil {
 		// Corrupt or empty database, init from scratch
 		log.Warn("Head block missing, resetting chain", "hash", head)
 		return bc.Reset()
 	}
 	// Everything seems to be fine, set as the head block
-	bc.currentBlock.Store(headBlock.Header())
+	bc.currentBlock.Store(headHeader)
 	headBlockGauge.Update(int64(headBlock.NumberU64()))
 
 	// Restore the last known head header
-	headHeader := headBlock.Header()
 	if head := rawdb.ReadHeadHeaderHash(bc.db); head != (common.Hash{}) {
 		if header := bc.GetHeaderByHash(head); header != nil {
 			headHeader = header
@@ -642,11 +656,15 @@ func (bc *BlockChain) SetHead(head uint64) error {
 	// Send chain head event to update the transaction pool
 	header := bc.CurrentBlock()
 	if block := bc.GetBlock(header.Hash(), header.Number.Uint64()); block == nil {
-		// This should never happen. In practice, previously currentBlock
-		// contained the entire block whereas now only a "marker", so there
-		// is an ever so slight chance for a race we should handle.
-		log.Error("Current block not found in database", "block", header.Number, "hash", header.Hash())
-		return fmt.Errorf("current block missing: #%d [%x..]", header.Number, header.Hash().Bytes()[:4])
+		// In a pruned node the genesis block will not exist in the freezer.
+		// It should not happen that we set head to any other pruned block.
+		if header.Number.Uint64() > 0 {
+			// This should never happen. In practice, previously currentBlock
+			// contained the entire block whereas now only a "marker", so there
+			// is an ever so slight chance for a race we should handle.
+			log.Error("Current block not found in database", "block", header.Number, "hash", header.Hash())
+			return fmt.Errorf("current block missing: #%d [%x..]", header.Number, header.Hash().Bytes()[:4])
+		}
 	}
 	bc.chainHeadFeed.Send(ChainHeadEvent{Header: header})
 	return nil
@@ -663,11 +681,15 @@ func (bc *BlockChain) SetHeadWithTimestamp(timestamp uint64) error {
 	// Send chain head event to update the transaction pool
 	header := bc.CurrentBlock()
 	if block := bc.GetBlock(header.Hash(), header.Number.Uint64()); block == nil {
-		// This should never happen. In practice, previously currentBlock
-		// contained the entire block whereas now only a "marker", so there
-		// is an ever so slight chance for a race we should handle.
-		log.Error("Current block not found in database", "block", header.Number, "hash", header.Hash())
-		return fmt.Errorf("current block missing: #%d [%x..]", header.Number, header.Hash().Bytes()[:4])
+		// In a pruned node the genesis block will not exist in the freezer.
+		// It should not happen that we set head to any other pruned block.
+		if header.Number.Uint64() > 0 {
+			// This should never happen. In practice, previously currentBlock
+			// contained the entire block whereas now only a "marker", so there
+			// is an ever so slight chance for a race we should handle.
+			log.Error("Current block not found in database", "block", header.Number, "hash", header.Hash())
+			return fmt.Errorf("current block missing: #%d [%x..]", header.Number, header.Hash().Bytes()[:4])
+		}
 	}
 	bc.chainHeadFeed.Send(ChainHeadEvent{Header: header})
 	return nil

core/txindexer.go

@@ -196,6 +196,19 @@ func (indexer *txIndexer) repair(head uint64) {
 	}
 }
 
+// resolveHead resolves the block number of the current chain head.
+func (indexer *txIndexer) resolveHead() uint64 {
+	headBlockHash := rawdb.ReadHeadBlockHash(indexer.db)
+	if headBlockHash == (common.Hash{}) {
+		return 0
+	}
+	headBlockNumber := rawdb.ReadHeaderNumber(indexer.db, headBlockHash)
+	if headBlockNumber == nil {
+		return 0
+	}
+	return *headBlockNumber
+}
+
 // loop is the scheduler of the indexer, assigning indexing/unindexing tasks depending
 // on the received chain event.
 func (indexer *txIndexer) loop(chain *BlockChain) {
@@ -203,9 +216,9 @@ func (indexer *txIndexer) loop(chain *BlockChain) {
 
 	// Listening to chain events and manipulate the transaction indexes.
 	var (
-		stop chan struct{}                                 // Non-nil if background routine is active
-		done chan struct{}                                 // Non-nil if background routine is active
-		head = rawdb.ReadHeadBlock(indexer.db).NumberU64() // The latest announced chain head
+		stop chan struct{}           // Non-nil if background routine is active
+		done chan struct{}           // Non-nil if background routine is active
+		head = indexer.resolveHead() // The latest announced chain head
 
 		headCh = make(chan ChainHeadEvent)
 		sub    = chain.SubscribeChainHeadEvent(headCh)

core/txpool/txpool.go

@@ -186,13 +186,15 @@ func (p *TxPool) loop(head *types.Header) {
 			// Try to inject a busy marker and start a reset if successful
 			select {
 			case resetBusy <- struct{}{}:
-				statedb, err := p.chain.StateAt(newHead.Root)
-				if err != nil {
-					log.Crit("Failed to reset txpool state", "err", err)
+				// Updates the statedb with the new chain head. The head state may be
+				// unavailable if the initial state sync has not yet completed.
+				if statedb, err := p.chain.StateAt(newHead.Root); err != nil {
+					log.Error("Failed to reset txpool state", "err", err)
+				} else {
+					p.stateLock.Lock()
+					p.state = statedb
+					p.stateLock.Unlock()
 				}
-				p.stateLock.Lock()
-				p.state = statedb
-				p.stateLock.Unlock()
 
 				// Busy marker injected, start a new subpool reset
 				go func(oldHead, newHead *types.Header) {