[3.5]Replace unnecessary Lock()/Unlock()s with RLock()/RUnlock()s

server/auth/store.go

@@ -332,8 +332,8 @@ func (as *authStore) CheckPassword(username, password string) (uint64, error) {
 	// to avoid putting it in the critical section of the tx lock.
 	revision, err := func() (uint64, error) {
 		tx := as.be.ReadTx()
-		tx.Lock()
-		defer tx.Unlock()
+		tx.RLock()
+		defer tx.RUnlock()
 
 		user = getUser(as.lg, tx, username)
 		if user == nil {
@@ -361,7 +361,7 @@ func (as *authStore) Recover(be backend.Backend) {
 	enabled := false
 	as.be = be
 	tx := be.ReadTx()
-	tx.Lock()
+	tx.RLock()
 	_, vs := tx.UnsafeRange(buckets.Auth, enableFlagKey, nil, 0)
 	if len(vs) == 1 {
 		if bytes.Equal(vs[0], authEnabled) {
@@ -372,7 +372,7 @@ func (as *authStore) Recover(be backend.Backend) {
 	as.setRevision(getRevision(tx))
 	as.refreshRangePermCache(tx)
 
-	tx.Unlock()
+	tx.RUnlock()
 
 	as.enabledMu.Lock()
 	as.enabled = enabled
@@ -858,8 +858,8 @@ func (as *authStore) isOpPermitted(userName string, revision uint64, key, rangeE
 	}
 
 	tx := as.be.ReadTx()
-	tx.Lock()
-	defer tx.Unlock()
+	tx.RLock()
+	defer tx.RUnlock()
 
 	user := getUser(as.lg, tx, userName)
 	if user == nil {
@@ -900,9 +900,9 @@ func (as *authStore) IsAdminPermitted(authInfo *AuthInfo) error {
 	}
 
 	tx := as.be.ReadTx()
-	tx.Lock()
+	tx.RLock()
 	u := getUser(as.lg, tx, authInfo.Username)
-	tx.Unlock()
+	tx.RUnlock()
 
 	if u == nil {
 		return ErrUserNotFound

server/etcdserver/api/membership/cluster.go

@@ -771,8 +771,8 @@ func clusterVersionFromBackend(lg *zap.Logger, be backend.Backend) *semver.Versi
 func downgradeInfoFromBackend(lg *zap.Logger, be backend.Backend) *DowngradeInfo {
 	dkey := backendDowngradeKey()
 	tx := be.ReadTx()
-	tx.Lock()
-	defer tx.Unlock()
+	tx.RLock()
+	defer tx.RUnlock()
 	keys, vals := tx.UnsafeRange(buckets.Cluster, dkey, nil, 0)
 	if len(keys) == 0 {
 		return nil

server/etcdserver/cindex/cindex.go

@@ -196,8 +196,8 @@ func unsafeReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
 // ReadConsistentIndex loads consistent index and term from given transaction.
 // returns 0 if the data are not found.
 func ReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
-	tx.Lock()
-	defer tx.Unlock()
+	tx.RLock()
+	defer tx.RUnlock()
 	return unsafeReadConsistentIndex(tx)
 }
 

server/mvcc/backend/read_tx.go

@@ -26,8 +26,13 @@ import (
 // is known to never overwrite any key so range is safe.
 
 type ReadTx interface {
+	// Lock and Unlock should only be used in the following three cases:
+	// 1. When committing a transaction. Because it will reset the read tx, including the buffer;
+	// 2. When writing the pending data back to read buf, because obviously no reading is allowed when writing the read buffer;
+	// 3. When performing defragmentation, because again it will reset the read tx, including the read buffer.
 	Lock()
 	Unlock()
+	// RLock and RUnlock should be used for all other cases.
 	RLock()
 	RUnlock()
 

server/mvcc/kvstore.go

@@ -230,8 +230,8 @@ func (s *store) updateCompactRev(rev int64) (<-chan struct{}, int64, error) {
 // checkPrevCompactionCompleted checks whether the previous scheduled compaction is completed.
 func (s *store) checkPrevCompactionCompleted() bool {
 	tx := s.b.ReadTx()
-	tx.Lock()
-	defer tx.Unlock()
+	tx.RLock()
+	defer tx.RUnlock()
 	_, scheduledCompactBytes := tx.UnsafeRange(buckets.Meta, scheduledCompactKeyName, nil, 0)
 	scheduledCompact := int64(0)
 	if len(scheduledCompactBytes) != 0 {
@@ -341,7 +341,7 @@ func (s *store) restore() error {
 
 	// restore index
 	tx := s.b.ReadTx()
-	tx.Lock()
+	tx.RLock()
 
 	_, finishedCompactBytes := tx.UnsafeRange(buckets.Meta, finishedCompactKeyName, nil, 0)
 	if len(finishedCompactBytes) != 0 {
@@ -403,7 +403,7 @@ func (s *store) restore() error {
 
 	for key, lid := range keyToLease {
 		if s.le == nil {
-			tx.Unlock()
+			tx.RUnlock()
 			panic("no lessor to attach lease")
 		}
 		err := s.le.Attach(lid, []lease.LeaseItem{{Key: key}})
@@ -416,7 +416,7 @@ func (s *store) restore() error {
 		}
 	}
 
-	tx.Unlock()
+	tx.RUnlock()
 
 	s.lg.Info("kvstore restored", zap.Int64("current-rev", s.currentRev))