QBFT: fix chain fork when emptyblockperiodseconds is enabled (#1669)

Authored-by: H.HSEL <26063868+hhsel@users.noreply.github.com>

consensus/istanbul/qbft/core/core.go

@@ -78,8 +78,9 @@ type core struct {
 	backlogs   map[common.Address]*prque.Prque
 	backlogsMu *sync.Mutex
 
-	current   *roundState
-	handlerWg *sync.WaitGroup
+	current      *roundState
+	currentMutex sync.Mutex
+	handlerWg    *sync.WaitGroup
 
 	roundChangeSet   *roundChangeSet
 	roundChangeTimer *time.Timer
@@ -116,6 +117,9 @@ func (c *core) IsCurrentProposal(blockHash common.Hash) bool {
 
 // startNewRound starts a new round. if round equals to 0, it means to starts a new sequence
 func (c *core) startNewRound(round *big.Int) {
+	c.currentMutex.Lock()
+	defer c.currentMutex.Unlock()
+
 	var logger log.Logger
 	if c.current == nil {
 		logger = c.logger.New("old.round", -1, "old.seq", 0)

consensus/istanbul/qbft/core/preprepare.go

@@ -34,6 +34,11 @@ import (
 // - extends PRE-PREPARE message with ROUND-CHANGE and PREPARE justification
 // - broadcast PRE-PREPARE message to other validators
 func (c *core) sendPreprepareMsg(request *Request) {
+	// c.current and c.valSet (checked in IsProposer()) is updated asynchronously in startNewRound(),
+	// need to prevent race condition with mutex
+	c.currentMutex.Lock()
+	defer c.currentMutex.Unlock()
+
 	logger := c.currentLogger(true, nil)
 
 	// If I'm the proposer and I have the same sequence with the proposal