[client] Fix race conditions (#2869)

* Fix concurrent map access in status

* Fix race when retrieving ctx state error

* Fix race when accessing service controller server instance

client/cmd/service.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"context"
+	"sync"
 
 	"github.com/kardianos/service"
 	log "github.com/sirupsen/logrus"
@@ -13,10 +14,11 @@ import (
 )
 
 type program struct {
-	ctx            context.Context
-	cancel         context.CancelFunc
-	serv           *grpc.Server
-	serverInstance *server.Server
+	ctx              context.Context
+	cancel           context.CancelFunc
+	serv             *grpc.Server
+	serverInstance   *server.Server
+	serverInstanceMu sync.Mutex
 }
 
 func newProgram(ctx context.Context, cancel context.CancelFunc) *program {

client/cmd/service_controller.go

@@ -61,7 +61,9 @@ func (p *program) Start(svc service.Service) error {
 		}
 		proto.RegisterDaemonServiceServer(p.serv, serverInstance)
 
+		p.serverInstanceMu.Lock()
 		p.serverInstance = serverInstance
+		p.serverInstanceMu.Unlock()
 
 		log.Printf("started daemon server: %v", split[1])
 		if err := p.serv.Serve(listen); err != nil {
@@ -72,6 +74,7 @@ func (p *program) Start(svc service.Service) error {
 }
 
 func (p *program) Stop(srv service.Service) error {
+	p.serverInstanceMu.Lock()
 	if p.serverInstance != nil {
 		in := new(proto.DownRequest)
 		_, err := p.serverInstance.Down(p.ctx, in)
@@ -79,6 +82,7 @@ func (p *program) Stop(srv service.Service) error {
 			log.Errorf("failed to stop daemon: %v", err)
 		}
 	}
+	p.serverInstanceMu.Unlock()
 
 	p.cancel()