Initialization must be completed before calling _vdpa_register_device()
since it can connect the device to the vDPA bus, so requests can arrive
after that call.

So for example vdpasim_net_work(), which uses the net->*_stats variables,
can be scheduled before they are initialized.

Let's move _vdpa_register_device() to the end of vdpasim_net_dev_add()
and add a comment to avoid future issues.

Fixes: 0899774cb360 ("vdpa_sim_net: vendor satistics")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---

Notes:
    I don't have a reproducer, but I became aware of this problem while
    I was changing the buffer allocation.
    
    In the block device, as soon as the device is registered, the driver
    sends several requests, and I guess this might happen for the net
    device as well.
    
    Thanks,
    Stefano

 drivers/vdpa/vdpa_sim/vdpa_sim_net.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
index 862f405362de..dfe2ce341803 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
@@ -466,16 +466,21 @@ static int vdpasim_net_dev_add(struct vdpa_mgmt_dev *mdev, const char *name,
 
 	vdpasim_net_setup_config(simdev, config);
 
-	ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_NET_VQ_NUM);
-	if (ret)
-		goto reg_err;
-
 	net = sim_to_net(simdev);
 
 	u64_stats_init(&net->tx_stats.syncp);
 	u64_stats_init(&net->rx_stats.syncp);
 	u64_stats_init(&net->cq_stats.syncp);
 
+	/*
+	 * Initialization must be completed before this call, since it can
+	 * connect the device to the vDPA bus, so requests can arrive after
+	 * this call.
+	 */
+	ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_NET_VQ_NUM);
+	if (ret)
+		goto reg_err;
+
 	return 0;
 
 reg_err:
-- 
2.39.2

On Thu, Mar 30, 2023 at 12:03 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> Initialization must be completed before calling _vdpa_register_device()
> since it can connect the device to the vDPA bus, so requests can arrive
> after that call.
>
> So for example vdpasim_net_work(), which uses the net->*_stats variables,
> can be scheduled before they are initialized.
>
> Let's move _vdpa_register_device() to the end of vdpasim_net_dev_add()
> and add a comment to avoid future issues.
>
> Fixes: 0899774cb360 ("vdpa_sim_net: vendor satistics")
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Acked-by: Jason Wang <jasowang@redhat.com>

This is needed for -stable.

Thanks

> ---
>
> Notes:
>     I don't have a reproducer, but I became aware of this problem while
>     I was changing the buffer allocation.
>
>     In the block device, as soon as the device is registered, the driver
>     sends several requests, and I guess this might happen for the net
>     device as well.
>
>     Thanks,
>     Stefano
>
>  drivers/vdpa/vdpa_sim/vdpa_sim_net.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> index 862f405362de..dfe2ce341803 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> @@ -466,16 +466,21 @@ static int vdpasim_net_dev_add(struct vdpa_mgmt_dev *mdev, const char *name,
>
>         vdpasim_net_setup_config(simdev, config);
>
> -       ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_NET_VQ_NUM);
> -       if (ret)
> -               goto reg_err;
> -
>         net = sim_to_net(simdev);
>
>         u64_stats_init(&net->tx_stats.syncp);
>         u64_stats_init(&net->rx_stats.syncp);
>         u64_stats_init(&net->cq_stats.syncp);
>
> +       /*
> +        * Initialization must be completed before this call, since it can
> +        * connect the device to the vDPA bus, so requests can arrive after
> +        * this call.
> +        */
> +       ret = _vdpa_register_device(&simdev->vdpa, VDPASIM_NET_VQ_NUM);
> +       if (ret)
> +               goto reg_err;
> +
>         return 0;
>
>  reg_err:
> --
> 2.39.2
>