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

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Message-ID: <20220805182715.GA17335@bytedance>
Date:   Fri, 5 Aug 2022 11:27:15 -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

On Fri, Aug 05, 2022 at 02:42:39PM +0200, Stefano Garzarella wrote:
> On Thu, Aug 04, 2022 at 04:44:47PM -0700, Peilin Ye wrote:
> > 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.
> 
> It could work, but should we set `sk->sk_err` and call sk_error_report() to
> wake up thread waiting on poll()?
> 
> Maybe the previous version is simpler.

Right, I forgot about sk_error_report().  Let us use the simpler version
then.

> > 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?
> 
> If you have time, feel free to send it.
> 
> Since it is a fix, I believe you can use the "net" tree. (Also for this
> patch).
> 
> Remember to put the "Fixes" tag that should be the same.

Sure, I will send them this week.  Thanks!

Peilin Ye