Re: [RFC PATCH v8 19/19] af_vsock: serialize writes to shared socket

[Stefano Garzarella]

On Wed, Apr 14, 2021 at 01:51:17PM +0300, Arseny Krasnov wrote:
> On 13.04.2021 15:47, Arseny Krasnov wrote:
> > This add logic, that serializes write access to single socket
> > by multiple threads. It is implemented be adding field with TID
> > of current writer. When writer tries to send something, it checks
> > that field is -1(free), else it sleep in the same way as waiting
> > for free space at peers' side.
> >
> > This implementation is PoC and not related to SEQPACKET close, so
> > i've placed it after whole patchset.
> >
> > Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
> > ---
> >  include/net/af_vsock.h   |  1 +
> >  net/vmw_vsock/af_vsock.c | 10 +++++++++-
> >  2 files changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > index 53d3f33dbdbf..786df80b9fc3 100644
> > --- a/include/net/af_vsock.h
> > +++ b/include/net/af_vsock.h
> > @@ -69,6 +69,7 @@ struct vsock_sock {
> >  	u64 buffer_size;
> >  	u64 buffer_min_size;
> >  	u64 buffer_max_size;
> > +	pid_t tid_owner;
> >
> >  	/* Private to transport. */
> >  	void *trans;
> > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > index 54bee7e643f4..d00f8c07a9d3 100644
> > --- a/net/vmw_vsock/af_vsock.c
> > +++ b/net/vmw_vsock/af_vsock.c
> > @@ -1765,7 +1765,9 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
> >  		ssize_t written;
> >
> >  		add_wait_queue(sk_sleep(sk), &wait);
> > -		while (vsock_stream_has_space(vsk) == 0 &&
> > +		while ((vsock_stream_has_space(vsk) == 0 ||
> > +			(vsk->tid_owner != current->pid &&
> > +			 vsk->tid_owner != -1)) &&
> >  		       sk->sk_err == 0 &&
> >  		       !(sk->sk_shutdown & SEND_SHUTDOWN) &&
> >  		       !(vsk->peer_shutdown & RCV_SHUTDOWN)) {
> > @@ -1796,6 +1798,8 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
> >  				goto out_err;
> >  			}
> >  		}
> > +
> > +		vsk->tid_owner = current->pid;
> >  		remove_wait_queue(sk_sleep(sk), &wait);
> >
> >  		/* These checks occur both as part of and after the loop
> > @@ -1852,7 +1856,10 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
> >  			err = total_written;
> >  	}
> >  out:
> > +	vsk->tid_owner = -1;
> >  	release_sock(sk);
> > +	sk->sk_write_space(sk);
> > +
> >  	return err;
> >  }
> >
> > @@ -2199,6 +2206,7 @@ static int vsock_create(struct net *net, struct socket *sock,
> >  		return -ENOMEM;
> >
> >  	vsk = vsock_sk(sk);
> > +	vsk->tid_owner = -1;
> This must be moved to '__vsock_create()'

Okay, I'll review the next version.

In order to backport this fix to stable branches I think is better to 
move at the beginning of this series or even out as a separate patch.

Thanks,
Stefano

> >  	if (sock->type == SOCK_DGRAM) {
> >  		ret = vsock_assign_transport(vsk, NULL);