mcs: fix potential data race in scheduling server (#8539)

close #8538

Signed-off-by: lhy1024 <[email protected]>

Co-authored-by: ti-chi-bot[bot] <108142056+ti-chi-bot[bot]@users.noreply.github.com>

pkg/mcs/scheduling/server/server.go

@@ -55,6 +55,7 @@ import (
 	"github.com/tikv/pd/pkg/storage/endpoint"
 	"github.com/tikv/pd/pkg/storage/kv"
 	"github.com/tikv/pd/pkg/utils/apiutil"
+	"github.com/tikv/pd/pkg/utils/etcdutil"
 	"github.com/tikv/pd/pkg/utils/grpcutil"
 	"github.com/tikv/pd/pkg/utils/logutil"
 	"github.com/tikv/pd/pkg/utils/memberutil"
@@ -193,7 +194,7 @@ func (s *Server) updateAPIServerMemberLoop() {
 		if !s.IsServing() {
 			continue
 		}
-		members, err := s.GetClient().MemberList(ctx)
+		members, err := etcdutil.ListEtcdMembers(ctx, s.GetClient())
 		if err != nil {
 			log.Warn("failed to list members", errs.ZapError(err))
 			continue
@@ -212,6 +213,11 @@ func (s *Server) updateAPIServerMemberLoop() {
 				cc, err := s.GetDelegateClient(ctx, s.GetTLSConfig(), ep.ClientURLs[0])
 				if err != nil {
 					log.Info("failed to get delegate client", errs.ZapError(err))
+					continue
+				}
+				if !s.IsServing() {
+					// double check
+					break
 				}
 				if s.cluster.SwitchAPIServerLeader(pdpb.NewPDClient(cc)) {
 					if status.Leader != curLeader {