2 files changed, 12 insertions, 10 deletions
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index b706438bd..6b3238d6b 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -425,20 +425,17 @@ func (e *endpoint) notifyAborted() {
 // cookies to accept connections.
 func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts *header.TCPSynOptions) {
 	defer ctx.synRcvdCount.dec()
-	defer func() {
-		e.mu.Lock()
-		e.decSynRcvdCount()
-		e.mu.Unlock()
-	}()
 	defer s.decRef()
 
 	n, err := ctx.createEndpointAndPerformHandshake(s, opts, &waiter.Queue{}, e.owner)
 	if err != nil {
 		e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
 		e.stats.FailedConnectionAttempts.Increment()
+		e.decSynRcvdCount()
 		return
 	}
 	ctx.removePendingEndpoint(n)
+	e.decSynRcvdCount()
 	n.startAcceptedLoop()
 	e.stack.Stats().TCP.PassiveConnectionOpenings.Increment()
 
@@ -456,7 +453,9 @@ func (e *endpoint) incSynRcvdCount() bool {
 }
 
 func (e *endpoint) decSynRcvdCount() {
+	e.mu.Lock()
 	e.synRcvdCount--
+	e.mu.Unlock()
 }
 
 func (e *endpoint) acceptQueueIsFull() bool {
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index a7149efd0..93a580bad 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -5131,6 +5131,7 @@ func TestKeepalive(t *testing.T) {
 }
 
 func executeHandshake(t *testing.T, c *context.Context, srcPort uint16, synCookieInUse bool) (irs, iss seqnum.Value) {
+	t.Helper()
 	// Send a SYN request.
 	irs = seqnum.Value(789)
 	c.SendPacket(nil, &context.Headers{
@@ -5175,6 +5176,7 @@ func executeHandshake(t *testing.T, c *context.Context, srcPort uint16, synCooki
 }
 
 func executeV6Handshake(t *testing.T, c *context.Context, srcPort uint16, synCookieInUse bool) (irs, iss seqnum.Value) {
+	t.Helper()
 	// Send a SYN request.
 	irs = seqnum.Value(789)
 	c.SendV6Packet(nil, &context.Headers{
@@ -5238,13 +5240,14 @@ func TestListenBacklogFull(t *testing.T) {
 
 	// Test acceptance.
 	// Start listening.
-	listenBacklog := 2
+	listenBacklog := 10
 	if err := c.EP.Listen(listenBacklog); err != nil {
 		t.Fatalf("Listen failed: %s", err)
 	}
 
-	for i := 0; i < listenBacklog; i++ {
-		executeHandshake(t, c, context.TestPort+uint16(i), false /*synCookieInUse */)
+	lastPortOffset := uint16(0)
+	for ; int(lastPortOffset) < listenBacklog; lastPortOffset++ {
+		executeHandshake(t, c, context.TestPort+lastPortOffset, false /*synCookieInUse */)
 	}
 
 	time.Sleep(50 * time.Millisecond)
@@ -5252,7 +5255,7 @@ func TestListenBacklogFull(t *testing.T) {
 	// Now execute send one more SYN. The stack should not respond as the backlog
 	// is full at this point.
 	c.SendPacket(nil, &context.Headers{
-		SrcPort: context.TestPort + 2,
+		SrcPort: context.TestPort + uint16(lastPortOffset),
 		DstPort: context.StackPort,
 		Flags:   header.TCPFlagSyn,
 		SeqNum:  seqnum.Value(789),
@@ -5293,7 +5296,7 @@ func TestListenBacklogFull(t *testing.T) {
 	}
 
 	// Now a new handshake must succeed.
-	executeHandshake(t, c, context.TestPort+2, false /*synCookieInUse */)
+	executeHandshake(t, c, context.TestPort+lastPortOffset, false /*synCookieInUse */)
 
 	newEP, _, err := c.EP.Accept(nil)
 	if err == tcpip.ErrWouldBlock {