core/state: fix flawed meter on storage reads

core/state/state_object.go

@@ -197,12 +197,24 @@ func (s *stateObject) GetCommittedState(db Database, key common.Hash) common.Has
 	}
 	// If no live objects are available, attempt to use snapshots
 	var (
-		enc []byte
-		err error
+		enc   []byte
+		err   error
+		meter *time.Duration
 	)
+	readStart := time.Now()
+	if metrics.EnabledExpensive {
+		// If the snap is 'under construction', the first lookup may fail. If that
+		// happens, we don't want to double-count the time elapsed. Thus this
+		// dance with the metering.
+		defer func() {
+			if meter != nil {
+				*meter += time.Since(readStart)
+			}
+		}()
+	}
 	if s.db.snap != nil {
 		if metrics.EnabledExpensive {
-			defer func(start time.Time) { s.db.SnapshotStorageReads += time.Since(start) }(time.Now())
+			meter = &s.db.SnapshotStorageReads
 		}
 		// If the object was destructed in *this* block (and potentially resurrected),
 		// the storage has been cleared out, and we should *not* consult the previous
@@ -217,8 +229,14 @@ func (s *stateObject) GetCommittedState(db Database, key common.Hash) common.Has
 	}
 	// If snapshot unavailable or reading from it failed, load from the database
 	if s.db.snap == nil || err != nil {
+		if meter != nil {
+			// If we already spent time checking the snapshot, account for it
+			// and reset the readStart
+			*meter += time.Since(readStart)
+			readStart = time.Now()
+		}
 		if metrics.EnabledExpensive {
-			defer func(start time.Time) { s.db.StorageReads += time.Since(start) }(time.Now())
+			meter = &s.db.StorageReads
 		}
 		if enc, err = s.getTrie(db).TryGet(key[:]); err != nil {
 			s.setError(err)