[MM-28397] Fix data race in SqlSupplier (#15419)

* Fix data race in SqlSupplier

* Add comment

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/sqlstore/supplier.go

@@ -115,7 +115,7 @@ type SqlSupplier struct {
 	lockedToMaster bool
 	context        context.Context
 	license        *model.License
-	licenseMutex   sync.Mutex
+	licenseMutex   sync.RWMutex
 }
 
 type TraceOnAdapter struct{}
@@ -330,7 +330,10 @@ func (ss *SqlSupplier) GetMaster() *gorp.DbMap {
 }
 
 func (ss *SqlSupplier) GetSearchReplica() *gorp.DbMap {
-	if ss.license == nil {
+	ss.licenseMutex.RLock()
+	license := ss.license
+	ss.licenseMutex.RUnlock()
+	if license == nil {
 		return ss.GetMaster()
 	}
 
@@ -343,7 +346,10 @@ func (ss *SqlSupplier) GetSearchReplica() *gorp.DbMap {
 }
 
 func (ss *SqlSupplier) GetReplica() *gorp.DbMap {
-	if len(ss.settings.DataSourceReplicas) == 0 || ss.lockedToMaster || ss.license == nil {
+	ss.licenseMutex.RLock()
+	license := ss.license
+	ss.licenseMutex.RUnlock()
+	if len(ss.settings.DataSourceReplicas) == 0 || ss.lockedToMaster || license == nil {
 		return ss.GetMaster()
 	}