5 files changed, 48 insertions, 1 deletions
diff --git a/pkg/flipcall/BUILD b/pkg/flipcall/BUILD
index bd1d614b6..c1e078c7c 100644
--- a/pkg/flipcall/BUILD
+++ b/pkg/flipcall/BUILD
@@ -18,6 +18,7 @@ go_library(
         "//pkg/abi/linux",
         "//pkg/log",
         "//pkg/memutil",
+        "//third_party/gvsync",
     ],
 )
 
diff --git a/pkg/flipcall/ctrl_futex.go b/pkg/flipcall/ctrl_futex.go
index d59159912..8390915a2 100644
--- a/pkg/flipcall/ctrl_futex.go
+++ b/pkg/flipcall/ctrl_futex.go
@@ -82,6 +82,7 @@ func (ep *Endpoint) ctrlWaitFirst() error {
 	*ep.dataLen() = w.Len()
 
 	// Return control to the client.
+	raceBecomeInactive()
 	if err := ep.futexSwitchToPeer(); err != nil {
 		return err
 	}
diff --git a/pkg/flipcall/flipcall.go b/pkg/flipcall/flipcall.go
index 991018684..386cee42c 100644
--- a/pkg/flipcall/flipcall.go
+++ b/pkg/flipcall/flipcall.go
@@ -180,7 +180,11 @@ const (
 // Preconditions: ep is a client Endpoint. ep.Connect(), ep.RecvFirst(),
 // ep.SendRecv(), and ep.SendLast() have never been called.
 func (ep *Endpoint) Connect() error {
-	return ep.ctrlConnect()
+	err := ep.ctrlConnect()
+	if err == nil {
+		raceBecomeActive()
+	}
+	return err
 }
 
 // RecvFirst blocks until the peer Endpoint calls Endpoint.SendRecv(), then
@@ -192,6 +196,7 @@ func (ep *Endpoint) RecvFirst() (uint32, error) {
 	if err := ep.ctrlWaitFirst(); err != nil {
 		return 0, err
 	}
+	raceBecomeActive()
 	recvDataLen := atomic.LoadUint32(ep.dataLen())
 	if recvDataLen > ep.dataCap {
 		return 0, fmt.Errorf("received packet with invalid datagram length %d (maximum %d)", recvDataLen, ep.dataCap)
@@ -218,9 +223,11 @@ func (ep *Endpoint) SendRecv(dataLen uint32) (uint32, error) {
 	// after ep.ctrlRoundTrip(), so if the peer is mutating it concurrently then
 	// they can only shoot themselves in the foot.
 	*ep.dataLen() = dataLen
+	raceBecomeInactive()
 	if err := ep.ctrlRoundTrip(); err != nil {
 		return 0, err
 	}
+	raceBecomeActive()
 	recvDataLen := atomic.LoadUint32(ep.dataLen())
 	if recvDataLen > ep.dataCap {
 		return 0, fmt.Errorf("received packet with invalid datagram length %d (maximum %d)", recvDataLen, ep.dataCap)
@@ -240,6 +247,7 @@ func (ep *Endpoint) SendLast(dataLen uint32) error {
 		panic(fmt.Sprintf("attempting to send packet with datagram length %d (maximum %d)", dataLen, ep.dataCap))
 	}
 	*ep.dataLen() = dataLen
+	raceBecomeInactive()
 	if err := ep.ctrlWakeLast(); err != nil {
 		return err
 	}
diff --git a/pkg/flipcall/flipcall_test.go b/pkg/flipcall/flipcall_test.go
index 435e4eeae..168a487ec 100644
--- a/pkg/flipcall/flipcall_test.go
+++ b/pkg/flipcall/flipcall_test.go
@@ -62,6 +62,9 @@ func (c *testConnection) destroy() {
 }
 
 func testSendRecv(t *testing.T, c *testConnection) {
+	// This shared variable is used to confirm that synchronization between
+	// flipcall endpoints is visible to the Go race detector.
+	state := 0
 	var serverRun sync.WaitGroup
 	serverRun.Add(1)
 	go func() {
@@ -71,11 +74,19 @@ func testSendRecv(t *testing.T, c *testConnection) {
 			t.Errorf("server Endpoint.RecvFirst() failed: %v", err)
 			return
 		}
+		state++
+		if state != 2 {
+			t.Errorf("shared state counter: got %d, wanted 2", state)
+		}
 		t.Logf("server Endpoint got packet 1, sending packet 2 and waiting for packet 3")
 		if _, err := c.serverEP.SendRecv(0); err != nil {
 			t.Errorf("server Endpoint.SendRecv() failed: %v", err)
 			return
 		}
+		state++
+		if state != 4 {
+			t.Errorf("shared state counter: got %d, wanted 4", state)
+		}
 		t.Logf("server Endpoint got packet 3")
 	}()
 	defer func() {
@@ -89,10 +100,18 @@ func testSendRecv(t *testing.T, c *testConnection) {
 	if err := c.clientEP.Connect(); err != nil {
 		t.Fatalf("client Endpoint.Connect() failed: %v", err)
 	}
+	state++
+	if state != 1 {
+		t.Errorf("shared state counter: got %d, wanted 1", state)
+	}
 	t.Logf("client Endpoint sending packet 1 and waiting for packet 2")
 	if _, err := c.clientEP.SendRecv(0); err != nil {
 		t.Fatalf("client Endpoint.SendRecv() failed: %v", err)
 	}
+	state++
+	if state != 3 {
+		t.Errorf("shared state counter: got %d, wanted 3", state)
+	}
 	t.Logf("client Endpoint got packet 2, sending packet 3")
 	if err := c.clientEP.SendLast(0); err != nil {
 		t.Fatalf("client Endpoint.SendLast() failed: %v", err)
diff --git a/pkg/flipcall/flipcall_unsafe.go b/pkg/flipcall/flipcall_unsafe.go
index 73e6eef29..a37952637 100644
--- a/pkg/flipcall/flipcall_unsafe.go
+++ b/pkg/flipcall/flipcall_unsafe.go
@@ -17,6 +17,8 @@ package flipcall
 import (
 	"reflect"
 	"unsafe"
+
+	"gvisor.dev/gvisor/third_party/gvsync"
 )
 
 // Packets consist of a 16-byte header followed by an arbitrarily-sized
@@ -67,3 +69,19 @@ func (ep *Endpoint) Data() []byte {
 	bsReflect.Cap = int(ep.dataCap)
 	return bs
 }
+
+// ioSync is a dummy variable used to indicate synchronization to the Go race
+// detector. Compare syscall.ioSync.
+var ioSync int64
+
+func raceBecomeActive() {
+	if gvsync.RaceEnabled {
+		gvsync.RaceAcquire((unsafe.Pointer)(&ioSync))
+	}
+}
+
+func raceBecomeInactive() {
+	if gvsync.RaceEnabled {
+		gvsync.RaceReleaseMerge((unsafe.Pointer)(&ioSync))
+	}
+}