net: fix testHookDialTCP race

CL 410754 introduces a race accessing the global testHookDialTCP hook.
Avoiding this race is difficult, since Dial can return while
goroutines it starts are still running. Add a version of this
hook to sysDialer, so it can be set on a per-test basis.

(Perhaps other uses of this hook should be moved to use the
sysDialer-local hook, but this change fixes the immediate data race.)

For #52173.

Change-Id: I8fb9be13957e91f92919cae7be213c38ad2af75a
Reviewed-on: https://go-review.googlesource.com/c/go/+/410957
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

4 files changed, 16 insertions, 10 deletions

diff --git a/src/net/dial.go b/src/net/dial.go
index b24bd2f5f4..c538342566 100644
--- a/src/net/dial.go
+++ b/src/net/dial.go
@@ -341,6 +341,7 @@ func DialTimeout(network, address string, timeout time.Duration) (Conn, error) {
 type sysDialer struct {
 	Dialer
 	network, address string
+	testHookDialTCP  func(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error)
 }
 
 // Dial connects to the address on the named network.
diff --git a/src/net/dial_test.go b/src/net/dial_test.go
index 0550acb01d..e49b4a61d6 100644
--- a/src/net/dial_test.go
+++ b/src/net/dial_test.go
@@ -234,9 +234,7 @@ func TestDialParallel(t *testing.T) {
 	for i, tt := range testCases {
 		i, tt := i, tt
 		t.Run(fmt.Sprint(i), func(t *testing.T) {
-			origTestHookDialTCP := testHookDialTCP
-			defer func() { testHookDialTCP = origTestHookDialTCP }()
-			testHookDialTCP = func(ctx context.Context, network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
+			dialTCP := func(ctx context.Context, network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
 				n := "tcp6"
 				if raddr.IP.To4() != nil {
 					n = "tcp4"
@@ -262,9 +260,10 @@ func TestDialParallel(t *testing.T) {
 			}
 			startTime := time.Now()
 			sd := &sysDialer{
-				Dialer:  d,
-				network: "tcp",
-				address: "?",
+				Dialer:          d,
+				network:         "tcp",
+				address:         "?",
+				testHookDialTCP: dialTCP,
 			}
 			c, err := sd.dialParallel(context.Background(), primaries, fallbacks)
 			elapsed := time.Since(startTime)
diff --git a/src/net/tcpsock_plan9.go b/src/net/tcpsock_plan9.go
index 768d03b06c..435335e92e 100644
--- a/src/net/tcpsock_plan9.go
+++ b/src/net/tcpsock_plan9.go
@@ -15,8 +15,11 @@ func (c *TCPConn) readFrom(r io.Reader) (int64, error) {
 }
 
 func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
-	if testHookDialTCP != nil {
-		return testHookDialTCP(ctx, sd.network, laddr, raddr)
+	if h := sd.testHookDialTCP; h != nil {
+		return h(ctx, sd.network, laddr, raddr)
+	}
+	if h := testHookDialTCP; h != nil {
+		return h(ctx, sd.network, laddr, raddr)
 	}
 	return sd.doDialTCP(ctx, laddr, raddr)
 }
diff --git a/src/net/tcpsock_posix.go b/src/net/tcpsock_posix.go
index bc3d324e6b..1c91170c50 100644
--- a/src/net/tcpsock_posix.go
+++ b/src/net/tcpsock_posix.go
@@ -55,8 +55,11 @@ func (c *TCPConn) readFrom(r io.Reader) (int64, error) {
 }
 
 func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
-	if testHookDialTCP != nil {
-		return testHookDialTCP(ctx, sd.network, laddr, raddr)
+	if h := sd.testHookDialTCP; h != nil {
+		return h(ctx, sd.network, laddr, raddr)
+	}
+	if h := testHookDialTCP; h != nil {
+		return h(ctx, sd.network, laddr, raddr)
 	}
 	return sd.doDialTCP(ctx, laddr, raddr)
 }