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

["Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" <longpeng2@huawei.com>]

Hi Stefano,

> -----Original Message-----
> From: Stefano Garzarella [mailto:sgarzare@redhat.com]
> Sent: Thursday, May 13, 2021 5:42 PM
> To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> <longpeng2@huawei.com>
> Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Gonglei (Arei)
> <arei.gonglei@huawei.com>; Subo (Subo, Cloud Infrastructure Service Product
> Dept.) <subo7@huawei.com>; David S . Miller <davem@davemloft.net>; Jakub
> Kicinski <kuba@kernel.org>; Jorgen Hansen <jhansen@vmware.com>; Norbert
> Slusarek <nslusarek@gmx.net>; Andra Paraschiv <andraprs@amazon.com>;
> Colin Ian King <colin.king@canonical.com>; David Brazdil
> <dbrazdil@google.com>; Alexander Popov <alex.popov@linux.com>;
> lixianming (E) <lixianming5@huawei.com>
> Subject: Re: [RFC] vsock: notify server to shutdown when client has pending
> signal
> 
> Hi,
> thanks for this patch, comments below...
> 
> On Tue, May 11, 2021 at 05:41:27PM +0800, Longpeng(Mike) wrote:
> >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);
> 
> I see the issue, but I'm not sure is okay to send the shutdown in any case,
> think about the server didn't setup the connection.
> 
> Maybe is better to set TCP_CLOSING if the socket state was TCP_ESTABLISHED,
> so the shutdown will be handled by the
> transport->release() as usual.
> 
> What do you think?
> 

Your method looks more gracefully, we'll try it and get back to you, thanks.

> Anyway, also without the patch, the server should receive a RST if it
> sends any data to the client, but of course, is better to let it know
> the socket is closed in advance.
> 

Yes, agree.

> Thanks,
> Stefano