From bb4f53342db1faf2e2a47aea169b07c056d6f058 Mon Sep 17 00:00:00 2001
From: Martin Holst Swende <martin@swende.se>
Date: Wed, 22 Sep 2021 18:36:42 +0200
Subject: [PATCH] eth/tracers: avoid unsyncronized mutations on trie database

---
 eth/state_accessor.go |  3 ++-
 eth/tracers/api.go    | 28 ++++++++++++++++++++--------
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/eth/state_accessor.go b/eth/state_accessor.go
index eb178311f30b7..ca2002b60dee2 100644
--- a/eth/state_accessor.go
+++ b/eth/state_accessor.go
@@ -119,7 +119,8 @@ func (eth *Ethereum) stateAtBlock(block *types.Block, reexec uint64, base *state
 		// Finalize the state so any modifications are written to the trie
 		root, err := statedb.Commit(eth.blockchain.Config().IsEIP158(current.Number()))
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("stateAtBlock commit failed, number %d root %v: %w",
+				current.NumberU64(), current.Root().Hex(), err)
 		}
 		statedb, err = state.New(root, database, nil)
 		if err != nil {
diff --git a/eth/tracers/api.go b/eth/tracers/api.go
index 68265932854cb..98961fe3d72e7 100644
--- a/eth/tracers/api.go
+++ b/eth/tracers/api.go
@@ -290,7 +290,11 @@ func (api *API) traceChain(ctx context.Context, start, end *types.Block, config
 		}()
 	}
 	// Start a goroutine to feed all the blocks into the tracers
-	begin := time.Now()
+	var (
+		begin     = time.Now()
+		derefTodo []common.Hash // list of hashes to dereference from the db
+		derefsMu  sync.Mutex    // mutex for the derefs
+	)
 
 	go func() {
 		var (
@@ -324,6 +328,14 @@ func (api *API) traceChain(ctx context.Context, start, end *types.Block, config
 				return
 			default:
 			}
+			// clean out any derefs
+			derefsMu.Lock()
+			for _, h := range derefTodo {
+				statedb.Database().TrieDB().Dereference(h)
+			}
+			derefTodo = derefTodo[:0]
+			derefsMu.Unlock()
+
 			// Print progress logs if long enough time elapsed
 			if time.Since(logged) > 8*time.Second {
 				logged = time.Now()
@@ -337,10 +349,11 @@ func (api *API) traceChain(ctx context.Context, start, end *types.Block, config
 			}
 			// Prepare the statedb for tracing. Don't use the live database for
 			// tracing to avoid persisting state junks into the database.
-			statedb, err = api.backend.StateAtBlock(localctx, block, reexec, statedb, false)
-			if err != nil {
+			if _statedb, err := api.backend.StateAtBlock(localctx, block, reexec, statedb, false); err != nil {
 				failed = err
 				break
+			} else {
+				statedb = _statedb
 			}
 			if statedb.Database().TrieDB() != nil {
 				// Hold the reference for tracer, will be released at the final stage
@@ -382,12 +395,11 @@ func (api *API) traceChain(ctx context.Context, start, end *types.Block, config
 				Hash:   res.block.Hash(),
 				Traces: res.results,
 			}
+			// Schedule any parent tries held in memory by this task for dereferencing
 			done[uint64(result.Block)] = result
-
-			// Dereference any parent tries held in memory by this task
-			if res.statedb.Database().TrieDB() != nil {
-				res.statedb.Database().TrieDB().Dereference(res.rootref)
-			}
+			derefsMu.Lock()
+			derefTodo = append(derefTodo, res.rootref)
+			derefsMu.Unlock()
 			// Stream completed traces to the user, aborting on the first error
 			for result, ok := done[next]; ok; result, ok = done[next] {
 				if len(result.Traces) > 0 || next == end.NumberU64() {