eth/tracers: avoid using blockCtx concurrently (ethereum#24286)

eth/tracers/api.go

@@ -601,11 +601,11 @@ func (api *API) traceBlock(ctx context.Context, block *types.Block, config *Trac
 	if threads > len(txs) {
 		threads = len(txs)
 	}
-	blockCtx := core.NewEVMBlockContext(block.Header(), api.chainContext(ctx), nil)
 	blockHash := block.Hash()
 	for th := 0; th < threads; th++ {
 		pend.Add(1)
 		go func() {
+			blockCtx := core.NewEVMBlockContext(block.Header(), api.chainContext(ctx), nil)
 			defer pend.Done()
 			// Fetch and execute the next transaction trace tasks
 			for task := range jobs {
@@ -626,6 +626,7 @@ func (api *API) traceBlock(ctx context.Context, block *types.Block, config *Trac
 	}
 	// Feed the transactions into the tracers and return
 	var failed error
+	blockCtx := core.NewEVMBlockContext(block.Header(), api.chainContext(ctx), nil)
 	for i, tx := range txs {
 		// Send the trace task over for execution
 		jobs <- &txTraceTask{statedb: statedb.Copy(), index: i}