linux-kernel - Re: [PATCH RFC net-next] vsock: Reschedule connect_work for O

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Message-ID: <20220804234447.GA2294@bytedance>
Date:   Thu, 4 Aug 2022 16:44:47 -0700
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Peilin Ye <peilin.ye@...edance.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC net-next] vsock: Reschedule connect_work for
 O_NONBLOCK connect() requests

Hi Stefano,

On Thu, Aug 04, 2022 at 08:59:23AM +0200, Stefano Garzarella wrote:
> The last thing I was trying to figure out before sending the patch was
> whether to set sock->state = SS_UNCONNECTED in vsock_connect_timeout().
> 
> I think we should do that, otherwise a subsequent to connect() with
> O_NONBLOCK set would keep returning -EALREADY, even though the timeout has
> expired.
> 
> What do you think?

Thanks for bringing this up, after thinking about sock->state, I have 3
thoughts:

1. I think the root cause of this memleak is, we keep @connect_work
   pending, even after the 2nd, blocking request times out (or gets
   interrupted) and sets sock->state back to SS_UNCONNECTED.

   @connect_work is effectively no-op when sk->sk_state is
   TCP_CLOS{E,ING} anyway, so why not we just cancel @connect_work when
   blocking requests time out or get interrupted?  Something like:

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index f04abf662ec6..62628af84164 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1402,6 +1402,9 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr,
                lock_sock(sk);

                if (signal_pending(current)) {
+                       if (cancel_delayed_work(&vsk->connect_work))
+                               sock_put(sk);
+
                        err = sock_intr_errno(timeout);
                        sk->sk_state = sk->sk_state == TCP_ESTABLISHED ? TCP_CLOSING : TCP_CLOSE;
                        sock->state = SS_UNCONNECTED;
@@ -1409,6 +1412,9 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr,
                        vsock_remove_connected(vsk);
                        goto out_wait;
                } else if (timeout == 0) {
+                       if (cancel_delayed_work(&vsk->connect_work))
+                               sock_put(sk);
+
                        err = -ETIMEDOUT;
                        sk->sk_state = TCP_CLOSE;
                        sock->state = SS_UNCONNECTED;

   Then no need to worry about rescheduling @connect_work, and the state
   machine becomes more accurate.  What do you think?  I will ask syzbot
   to test this.

2. About your suggestion of setting sock->state = SS_UNCONNECTED in
   vsock_connect_timeout(), I think it makes sense.  Are you going to
   send a net-next patch for this?

3. After a TCP_SYN_SENT sock receives VIRTIO_VSOCK_OP_RESPONSE in
   virtio_transport_recv_connecting(), why don't we cancel @connect_work?
   Am I missing something?

Thanks,
Peilin Ye