Fix race condition (*tcp.endpoint).Close

Atomically close the endpoint. Before this change, it was possible for
multiple callers to perform duplicate work.

PiperOrigin-RevId: 300462110

pkg/tcpip/transport/tcp/endpoint.go

@@ -825,6 +825,7 @@ func (e *endpoint) Abort() {
 func (e *endpoint) Close() {
 	e.mu.Lock()
 	closed := e.closed
+	e.closed = true
 	e.mu.Unlock()
 	if closed {
 		return
@@ -833,13 +834,7 @@ func (e *endpoint) Close() {
 	// Issue a shutdown so that the peer knows we won't send any more data
 	// if we're connected, or stop accepting if we're listening.
 	e.Shutdown(tcpip.ShutdownWrite | tcpip.ShutdownRead)
-	e.closeNoShutdown()
-}
 
-// closeNoShutdown closes the endpoint without doing a full shutdown. This is
-// used when a connection needs to be aborted with a RST and we want to skip
-// a full 4 way TCP shutdown.
-func (e *endpoint) closeNoShutdown() {
 	e.mu.Lock()
 
 	// For listening sockets, we always release ports inline so that they
@@ -858,8 +853,6 @@ func (e *endpoint) closeNoShutdown() {
 		e.boundPortFlags = ports.Flags{}
 	}
 
-	// Mark endpoint as closed.
-	e.closed = true
 	// Either perform the local cleanup or kick the worker to make sure it
 	// knows it needs to cleanup.
 	switch e.EndpointState() {