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

[Stefano Garzarella]

On Mon, May 17, 2021 at 02:18:51AM +0000, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
> Hi Stefano,
>
> > -----Original Message-----
> > From: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > [mailto:longpeng2@xxxxxxxxxx]
> > Sent: Thursday, May 13, 2021 6:36 PM
> > To: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Gonglei (Arei)
> > <arei.gonglei@xxxxxxxxxx>; Subo (Subo, Cloud Infrastructure Service Product
> > Dept.) <subo7@xxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Jakub
> > Kicinski <kuba@xxxxxxxxxx>; Jorgen Hansen <jhansen@xxxxxxxxxx>; Norbert
> > Slusarek <nslusarek@xxxxxxx>; Andra Paraschiv <andraprs@xxxxxxxxxx>;
> > Colin Ian King <colin.king@xxxxxxxxxxxxx>; David Brazdil
> > <dbrazdil@xxxxxxxxxx>; Alexander Popov <alex.popov@xxxxxxxxx>;
> > lixianming (E) <lixianming5@xxxxxxxxxx>
> > Subject: RE: [RFC] vsock: notify server to shutdown when client has pending
> > signal
> >
> > Hi Stefano,
> >
> > > -----Original Message-----
> > > From: Stefano Garzarella [mailto:sgarzare@xxxxxxxxxx]
> > > Sent: Thursday, May 13, 2021 5:42 PM
> > > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
> > > <longpeng2@xxxxxxxxxx>
> > > Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Gonglei
> > > (Arei) <arei.gonglei@xxxxxxxxxx>; Subo (Subo, Cloud Infrastructure
> > > Service Product
> > > Dept.) <subo7@xxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>;
> > > Jakub Kicinski <kuba@xxxxxxxxxx>; Jorgen Hansen <jhansen@xxxxxxxxxx>;
> > > Norbert Slusarek <nslusarek@xxxxxxx>; Andra Paraschiv
> > > <andraprs@xxxxxxxxxx>; Colin Ian King <colin.king@xxxxxxxxxxxxx>;
> > > David Brazdil <dbrazdil@xxxxxxxxxx>; Alexander Popov
> > > <alex.popov@xxxxxxxxx>; lixianming (E) <lixianming5@xxxxxxxxxx>
> > > 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@xxxxxxxxxxxxx>
> > > >Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> > > >Cc: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > > >Cc: Jorgen Hansen <jhansen@xxxxxxxxxx>
> > > >Cc: Norbert Slusarek <nslusarek@xxxxxxx>
> > > >Cc: Andra Paraschiv <andraprs@xxxxxxxxxx>
> > > >Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > > >Cc: David Brazdil <dbrazdil@xxxxxxxxxx>
> > > >Cc: Alexander Popov <alex.popov@xxxxxxxxx>
> > > >Signed-off-by: lixianming <lixianming5@xxxxxxxxxx>
> > > >Signed-off-by: Longpeng(Mike) <longpeng2@xxxxxxxxxx>
> > > >---
> > > > 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.
>
> As your suggestion, the following code can solve the problem:
>
>                if (signal_pending(current)) {
>                        err = sock_intr_errno(timeout);
> -                       sk->sk_state = TCP_CLOSE;
> +                       sk->sk_state = TCP_CLOSING;
>                        sock->state = SS_UNCONNECTED;
>                        vsock_transport_cancel_pkt(vsk);
>                        goto out_wait;
>
> This will send shutdown to the server even if the connection is not established, but
> I don't see any side effects yet, right ?

Should we set TCP_CLOSING only if sk_state was TCP_ESTABLISHED?

> The problem is also in the timeout case, we should fix it together ?

I'm not sure, if we reach the timeout, it should mean that the other 
peer never answered, so why take care to notify it?

Thanks,
Stefano