[RFC] vsock: notify server to shutdown when client has pending signal

["Longpeng(Mike)" <longpeng2@huawei.com>]

The client's sk_state will be set to TCP_ESTABLISHED if the
server replay the client's connect request.
However, if the client has pending signal, its sk_state will
be set to TCP_CLOSE without notify the server, so the server
will hold the corrupt connection.

            client                        server

1. sk_state=TCP_SYN_SENT         |
2. call ->connect()              |
3. wait reply                    |
                                 | 4. sk_state=TCP_ESTABLISHED
                                 | 5. insert to connected list
                                 | 6. reply to the client
7. sk_state=TCP_ESTABLISHED      |
8. insert to connected list      |
9. *signal pending* <--------------------- the user kill client
10. sk_state=TCP_CLOSE           |
client is exiting...             |
11. call ->release()             |
     virtio_transport_close
      if (!(sk->sk_state == TCP_ESTABLISHED ||
	      sk->sk_state == TCP_CLOSING))
		return true; <------------- return at here
As a result, the server cannot notice the connection is corrupt.
So the client should notify the peer in this case.

Cc: David S. Miller <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Stefano Garzarella <sgarzare@redhat.com>
Cc: Jorgen Hansen <jhansen@vmware.com>
Cc: Norbert Slusarek <nslusarek@gmx.net>
Cc: Andra Paraschiv <andraprs@amazon.com>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: David Brazdil <dbrazdil@google.com>
Cc: Alexander Popov <alex.popov@linux.com>
Signed-off-by: lixianming <lixianming5@huawei.com>
Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
 net/vmw_vsock/af_vsock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 92a72f0..d5df908 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1368,6 +1368,7 @@ static int vsock_stream_connect(struct socket *sock, struct sockaddr *addr,
 		lock_sock(sk);
 
 		if (signal_pending(current)) {
+			vsock_send_shutdown(sk, SHUTDOWN_MASK);
 			err = sock_intr_errno(timeout);
 			sk->sk_state = TCP_CLOSE;
 			sock->state = SS_UNCONNECTED;
-- 
1.8.3.1