Re: [RFC PATCH v4 2/3] virtio/vsock: send credit update during setting SO_RCVLOWAT

[Arseniy Krasnov]

On 30.11.2023 11:38, Stefano Garzarella wrote:
> On Thu, Nov 30, 2023 at 12:25:18AM +0300, Arseniy Krasnov wrote:
>> Send 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>
>> ---
>> Changelog:
>> v1 -> v2:
>>  * Update commit message by removing 'This patch adds XXX' manner.
>>  * Do not initialize 'send_update' variable - set it directly during
>>    first usage.
>> v3 -> v4:
>>  * Fit comment in 'virtio_transport_notify_set_rcvlowat()' to 80 chars.
>>
>> drivers/vhost/vsock.c                   |  3 ++-
>> include/linux/virtio_vsock.h            |  1 +
>> net/vmw_vsock/virtio_transport.c        |  3 ++-
>> net/vmw_vsock/virtio_transport_common.c | 27 +++++++++++++++++++++++++
>> net/vmw_vsock/vsock_loopback.c          |  3 ++-
>> 5 files changed, 34 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> index f75731396b7e..c5e58a60a546 100644
>> --- a/drivers/vhost/vsock.c
>> +++ b/drivers/vhost/vsock.c
>> @@ -449,8 +449,9 @@ static struct virtio_transport vhost_transport = {
>>         .notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
>>         .notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
>>         .notify_buffer_size       = virtio_transport_notify_buffer_size,
>> +        .notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
>>
>> -        .read_skb = virtio_transport_read_skb,
>> +        .read_skb = virtio_transport_read_skb
> 
> I think it is better to avoid this change, so when we will need to add
> new callbacks, we don't need to edit this line again.
> 
> Please avoid it also in the other place in this patch.
> 
> The rest LGTM.

Yes, I see, I thought about that, but chose beauty instead of pragmatism :)
Ok, I'll fix it:)

Thanks, Arseniy

> 
> Thanks,
> Stefano
> 
>>     },
>>
>>     .send_pkt = vhost_transport_send_pkt,
>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> index ebb3ce63d64d..c82089dee0c8 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_notify_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..8b7bb7ca8ea5 100644
>> --- a/net/vmw_vsock/virtio_transport.c
>> +++ b/net/vmw_vsock/virtio_transport.c
>> @@ -537,8 +537,9 @@ static struct virtio_transport virtio_transport = {
>>         .notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
>>         .notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
>>         .notify_buffer_size       = virtio_transport_notify_buffer_size,
>> +        .notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
>>
>> -        .read_skb = virtio_transport_read_skb,
>> +        .read_skb = virtio_transport_read_skb
>>     },
>>
>>     .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 f6dc896bf44c..1cb556ad4597 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -1684,6 +1684,33 @@ 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_notify_set_rcvlowat(struct vsock_sock *vsk, int val)
>> +{
>> +    struct virtio_vsock_sock *vvs = vsk->trans;
>> +    bool send_update;
>> +
>> +    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.
>> +     */
>> +    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;
>> +    }
>> +
>> +    return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(virtio_transport_notify_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..454f69838c2a 100644
>> --- a/net/vmw_vsock/vsock_loopback.c
>> +++ b/net/vmw_vsock/vsock_loopback.c
>> @@ -96,8 +96,9 @@ static struct virtio_transport loopback_transport = {
>>         .notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
>>         .notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
>>         .notify_buffer_size       = virtio_transport_notify_buffer_size,
>> +        .notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
>>
>> -        .read_skb = virtio_transport_read_skb,
>> +        .read_skb = virtio_transport_read_skb
>>     },
>>
>>     .send_pkt = vsock_loopback_send_pkt,
>> -- 
>> 2.25.1
>>
>