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

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Date:   Wed, 14 Apr 2021 13:51:17 +0300
From:   Arseny Krasnov <arseny.krasnov@...persky.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Colin Ian King <colin.king@...onical.com>,
        Norbert Slusarek <nslusarek@....net>,
        Andra Paraschiv <andraprs@...zon.com>,
        Jeff Vander Stoep <jeffv@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v8 19/19] af_vsock: serialize writes to shared socket


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@...persky.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);