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

[Arseny Krasnov <arseny.krasnov@kaspersky.com>]

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@kaspersky.com>
> ---
>  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()'
>  
>  	if (sock->type == SOCK_DGRAM) {
>  		ret = vsock_assign_transport(vsk, NULL);