netdev - Re: [PATCH net] vsock/virtio: enable VQs early on probe

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Message-ID: <20220322140500.bn5yrqj5ljckhcdb@sgarzare-redhat>
Date:   Tue, 22 Mar 2022 15:05:00 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] vsock/virtio: enable VQs early on probe

On Tue, Mar 22, 2022 at 09:36:14AM -0400, Michael S. Tsirkin wrote:
>On Tue, Mar 22, 2022 at 11:38:23AM +0100, Stefano Garzarella wrote:
>> virtio spec requires drivers to set DRIVER_OK before using VQs.
>> This is set automatically after probe returns, but virtio-vsock
>> driver uses VQs in the probe function to fill rx and event VQs
>> with new buffers.
>
>
>So this is a spec violation. absolutely.
>
>> Let's fix this, calling virtio_device_ready() before using VQs
>> in the probe function.
>>
>> Fixes: 0ea9e1d3a9e3 ("VSOCK: Introduce virtio_transport.ko")
>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>> ---
>>  net/vmw_vsock/virtio_transport.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>> index 5afc194a58bb..b1962f8cd502 100644
>> --- a/net/vmw_vsock/virtio_transport.c
>> +++ b/net/vmw_vsock/virtio_transport.c
>> @@ -622,6 +622,8 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>>  	INIT_WORK(&vsock->event_work, virtio_transport_event_work);
>>  	INIT_WORK(&vsock->send_pkt_work, virtio_transport_send_pkt_work);
>>
>> +	virtio_device_ready(vdev);
>> +
>>  	mutex_lock(&vsock->tx_lock);
>>  	vsock->tx_run = true;
>>  	mutex_unlock(&vsock->tx_lock);
>
>Here's the whole code snippet:
>
>
>        mutex_lock(&vsock->tx_lock);
>        vsock->tx_run = true;
>        mutex_unlock(&vsock->tx_lock);
>
>        mutex_lock(&vsock->rx_lock);
>        virtio_vsock_rx_fill(vsock);
>        vsock->rx_run = true;
>        mutex_unlock(&vsock->rx_lock);
>
>        mutex_lock(&vsock->event_lock);
>        virtio_vsock_event_fill(vsock);
>        vsock->event_run = true;
>        mutex_unlock(&vsock->event_lock);
>
>        if (virtio_has_feature(vdev, VIRTIO_VSOCK_F_SEQPACKET))
>                vsock->seqpacket_allow = true;
>
>        vdev->priv = vsock;
>        rcu_assign_pointer(the_virtio_vsock, vsock);
>
>        mutex_unlock(&the_virtio_vsock_mutex);
>
>
>I worry that this is not the only problem here:
>seqpacket_allow and setting of vdev->priv at least after
>device is active look suspicious.

Right, so if you agree I'll move these before virtio_device_ready().

>E.g.:
>
>static void virtio_vsock_event_done(struct virtqueue *vq)
>{
>        struct virtio_vsock *vsock = vq->vdev->priv;
>
>        if (!vsock)
>                return;
>        queue_work(virtio_vsock_workqueue, &vsock->event_work);
>}
>
>looks like it will miss events now they will be reported earlier.
>One might say that since vq has been kicked it might send
>interrupts earlier too so not a new problem, but
>there's a chance device actually waits until DRIVER_OK
>to start operating.

Yes I see, should I break into 2 patches (one where I move the code 
already present and this one)?

Maybe a single patch is fine since it's the complete solution.

Thank you for the detailed explanation,
Stefano