etcdserver/api/v3rpc: hold lock when setting grpclog

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

etcdserver/api/v3rpc/grpc.go

@@ -19,6 +19,7 @@ import (
 	"io/ioutil"
 	"math"
 	"os"
+	"sync"
 
 	"github.com/coreos/etcd/etcdserver"
 	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
@@ -37,6 +38,8 @@ const (
 	maxSendBytes      = math.MaxInt32
 )
 
+var grpclogMu sync.Mutex
+
 func Server(s *etcdserver.EtcdServer, tls *tls.Config, gopts ...grpc.ServerOption) *grpc.Server {
 	var opts []grpc.ServerOption
 	opts = append(opts, grpc.CustomCodec(&codec{}))
@@ -67,6 +70,7 @@ func Server(s *etcdserver.EtcdServer, tls *tls.Config, gopts ...grpc.ServerOptio
 	// set zero values for metrics registered for this grpc server
 	grpc_prometheus.Register(grpcServer)
 
+	grpclogMu.Lock()
 	if s.Cfg.Debug {
 		grpc.EnableTracing = true
 		// enable info, warning, error
@@ -75,5 +79,7 @@ func Server(s *etcdserver.EtcdServer, tls *tls.Config, gopts ...grpc.ServerOptio
 		// only discard info
 		grpclog.SetLoggerV2(grpclog.NewLoggerV2(ioutil.Discard, os.Stderr, os.Stderr))
 	}
+	grpclogMu.Unlock()
+
 	return grpcServer
 }