Avoid deadlock in etcd.Close when stopping during bootstrapping

server/embed/etcd.go

@@ -84,6 +84,7 @@ type Etcd struct {
 	errc  chan error
 
 	closeOnce sync.Once
+	wg        sync.WaitGroup
 }
 
 type peerListener struct {
@@ -109,7 +110,7 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		if !serving {
 			// errored before starting gRPC server for serveCtx.serversC
 			for _, sctx := range e.sctxs {
-				close(sctx.serversC)
+				sctx.close()
 			}
 		}
 		e.Close()
@@ -456,6 +457,7 @@ func (e *Etcd) Close() {
 		}
 	}
 	if e.errc != nil {
+		e.wg.Wait()
 		close(e.errc)
 	}
 }
@@ -870,6 +872,9 @@ func (e *Etcd) serveMetrics() (err error) {
 }
 
 func (e *Etcd) errHandler(err error) {
+	e.wg.Add(1)
+	defer e.wg.Done()
+
 	if err != nil {
 		e.GetLogger().Error("setting up serving from embedded etcd failed.", zap.Error(err))
 	}

server/embed/serve.go

@@ -23,6 +23,7 @@ import (
 	"net"
 	"net/http"
 	"strings"
+	"sync"
 
 	gw "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
 	"github.com/soheilhy/cmux"
@@ -66,6 +67,7 @@ type serveCtx struct {
 	userHandlers    map[string]http.Handler
 	serviceRegister func(*grpc.Server)
 	serversC        chan *servers
+	closeOnce       sync.Once
 }
 
 type servers struct {
@@ -102,6 +104,9 @@ func (sctx *serveCtx) serve(
 ) (err error) {
 	logger := defaultLog.New(io.Discard, "etcdhttp", 0)
 
+	// Make sure serversC is closed even if we prematurely exit the function.
+	defer sctx.close()
+
 	select {
 	case <-s.StoppingNotify():
 		return errors.New("server is stopping")
@@ -121,8 +126,6 @@ func (sctx *serveCtx) serve(
 	servElection := v3election.NewElectionServer(v3c)
 	servLock := v3lock.NewLockServer(v3c)
 
-	// Make sure serversC is closed even if we prematurely exit the function.
-	defer close(sctx.serversC)
 	var gwmux *gw.ServeMux
 	if s.Cfg.EnableGRPCGateway {
 		// GRPC gateway connects to grpc server via connection provided by grpc dial.
@@ -521,3 +524,9 @@ func (sctx *serveCtx) registerTrace() {
 	evf := func(w http.ResponseWriter, r *http.Request) { trace.RenderEvents(w, r, true) }
 	sctx.registerUserHandler("/debug/events", http.HandlerFunc(evf))
 }
+
+func (sctx *serveCtx) close() {
+	sctx.closeOnce.Do(func() {
+		close(sctx.serversC)
+	})
+}

server/etcdserver/server.go

@@ -1776,6 +1776,7 @@ func (s *EtcdServer) publishV3(timeout time.Duration) {
 			ClientUrls: s.attributes.ClientURLs,
 		},
 	}
+	// gofail: var beforePublishing struct{}
 	lg := s.Logger()
 	for {
 		select {

tests/integration/embed/embed_test.go

@@ -219,3 +219,45 @@ func TestEmbedEtcdAutoCompactionRetentionRetained(t *testing.T) {
 	assert.Equal(t, durationToCompare, autoCompactionRetention)
 	e.Close()
 }
+
+func TestEmbedEtcdStopDuringBootstrapping(t *testing.T) {
+	integration2.BeforeTest(t, integration2.WithFailpoint("beforePublishing", `sleep("2s")`))
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+
+		cfg := embed.NewConfig()
+		urls := newEmbedURLs(false, 2)
+		setupEmbedCfg(cfg, []url.URL{urls[0]}, []url.URL{urls[1]})
+		cfg.Dir = filepath.Join(t.TempDir(), "embed-etcd")
+
+		e, err := embed.StartEtcd(cfg)
+		if err != nil {
+			t.Errorf("Failed to start etcd, got error %v", err)
+		}
+		defer e.Close()
+
+		go func() {
+			time.Sleep(time.Second)
+			e.Server.Stop()
+			t.Log("Stopped server during bootstrapping")
+		}()
+
+		select {
+		case <-e.Server.ReadyNotify():
+			t.Log("Server is ready!")
+		case <-e.Server.StopNotify():
+			t.Log("Server is stopped")
+		case <-time.After(20 * time.Second):
+			e.Server.Stop() // trigger a shutdown
+			t.Error("Server took too long to start!")
+		}
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(10 * time.Second):
+		t.Error("timeout in bootstrapping etcd")
+	}
+}