Re: [RFC PATCH v1 1/2] virtio/vsock: send credit update during setting SO_RCVLOWAT

[Stefano Garzarella]

On Wed, Nov 08, 2023 at 10:20:03AM +0300, Arseniy Krasnov wrote:
> This adds sending credit update message when SO_RCVLOWAT is updated and
> it is bigger than number of bytes in rx queue. It is needed, because
> 'poll()' will wait until number of bytes in rx queue will be not smaller
> than SO_RCVLOWAT, so kick sender to send more data. Otherwise mutual
> hungup for tx/rx is possible: sender waits for free space and receiver
> is waiting data in 'poll()'.
>
> Signed-off-by: Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxxxxx>
> ---
> drivers/vhost/vsock.c                   |  2 ++
> include/linux/virtio_vsock.h            |  1 +
> net/vmw_vsock/virtio_transport.c        |  2 ++
> net/vmw_vsock/virtio_transport_common.c | 31 +++++++++++++++++++++++++
> net/vmw_vsock/vsock_loopback.c          |  2 ++
> 5 files changed, 38 insertions(+)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index f75731396b7e..ecfa5c11f5ee 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -451,6 +451,8 @@ static struct virtio_transport vhost_transport = {
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>
> 		.read_skb = virtio_transport_read_skb,
> +
> +		.set_rcvlowat             = virtio_transport_set_rcvlowat
> 	},
>
> 	.send_pkt = vhost_transport_send_pkt,
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index ebb3ce63d64d..97dc1bebc69c 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -256,4 +256,5 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
> void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
> int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list);
> int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor);
> +int virtio_transport_set_rcvlowat(struct vsock_sock *vsk, int val);
> #endif /* _LINUX_VIRTIO_VSOCK_H */
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index af5bab1acee1..cf3431189d0c 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -539,6 +539,8 @@ static struct virtio_transport virtio_transport = {
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>
> 		.read_skb = virtio_transport_read_skb,
> +
> +		.set_rcvlowat             = virtio_transport_set_rcvlowat
> 	},
>
> 	.send_pkt = virtio_transport_send_pkt,
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index e22c81435ef7..88a58163046e 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -1676,6 +1676,37 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
> }
> EXPORT_SYMBOL_GPL(virtio_transport_read_skb);
>
> +int virtio_transport_set_rcvlowat(struct vsock_sock *vsk, int val)
> +{
> +	struct virtio_vsock_sock *vvs = vsk->trans;
> +	bool send_update = false;

I'd declare this not initialized.

> +
> +	spin_lock_bh(&vvs->rx_lock);
> +
> +	/* If number of available bytes is less than new
> +	 * SO_RCVLOWAT value, kick sender to send more
> +	 * data, because sender may sleep in its 'send()'
> +	 * syscall waiting for enough space at our side.
> +	 */
> +	if (vvs->rx_bytes < val)
> +		send_update = true;

Then here just:
	send_update = vvs->rx_bytes < val;

> +
> +	spin_unlock_bh(&vvs->rx_lock);
> +
> +	if (send_update) {
> +		int err;
> +
> +		err = virtio_transport_send_credit_update(vsk);
> +		if (err < 0)
> +			return err;
> +	}
> +
> +	WRITE_ONCE(sk_vsock(vsk)->sk_rcvlowat, val ? : 1);

Not in this patch, but what about doing this in vsock_set_rcvlowat() in 
af_vsock.c?

I mean avoid to return if `transport->set_rcvlowat(vsk, val)` is
successfully, so set sk_rcvlowat in a single point.

The rest LGTM!

Stefano

> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(virtio_transport_set_rcvlowat);
> +
> MODULE_LICENSE("GPL v2");
> MODULE_AUTHOR("Asias He");
> MODULE_DESCRIPTION("common code for virtio vsock");
> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> index 048640167411..388c157f6633 100644
> --- a/net/vmw_vsock/vsock_loopback.c
> +++ b/net/vmw_vsock/vsock_loopback.c
> @@ -98,6 +98,8 @@ static struct virtio_transport loopback_transport = {
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>
> 		.read_skb = virtio_transport_read_skb,
> +
> +		.set_rcvlowat             = virtio_transport_set_rcvlowat
> 	},
>
> 	.send_pkt = vsock_loopback_send_pkt,
> -- 2.25.1