netdev - Re: [PATCH net] virtio-net: set queues after driver

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Date: Wed, 9 Aug 2023 06:22:51 +0000
From: Dragos Tatulea <dtatulea@...dia.com>
To: "jasowang@...hat.com" <jasowang@...hat.com>, "mst@...hat.com"
	<mst@...hat.com>, "xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>
CC: "virtualization@...ts.linux-foundation.org"
	<virtualization@...ts.linux-foundation.org>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "davem@...emloft.net" <davem@...emloft.net>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] virtio-net: set queues after driver_ok

On Tue, 2023-08-08 at 23:13 -0400, Jason Wang wrote:
> Commit 25266128fe16 ("virtio-net: fix race between set queues and
> probe") tries to fix the race between set queues and probe by calling
> _virtnet_set_queues() before DRIVER_OK is set. This violates virtio
> spec. Fixing this by setting queues after virtio_device_ready().
> 
> Fixes: 25266128fe16 ("virtio-net: fix race between set queues and probe")
> Reported-by: Dragos Tatulea <dtatulea@...dia.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> The patch is needed for -stable.
> ---
>  drivers/net/virtio_net.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 1270c8d23463..ff03921e46df 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4219,8 +4219,6 @@ static int virtnet_probe(struct virtio_device *vdev)
>         if (vi->has_rss || vi->has_rss_hash_report)
>                 virtnet_init_default_rss(vi);
>  
> -       _virtnet_set_queues(vi, vi->curr_queue_pairs);
> -
>         /* serialize netdev register + virtio_device_ready() with ndo_open()
> */
>         rtnl_lock();
>  
> @@ -4233,6 +4231,8 @@ static int virtnet_probe(struct virtio_device *vdev)
>  
>         virtio_device_ready(vdev);
>  
> +       _virtnet_set_queues(vi, vi->curr_queue_pairs);
> +
>         /* a random MAC address has been assigned, notify the device.
>          * We don't fail probe if VIRTIO_NET_F_CTRL_MAC_ADDR is not there
>          * because many devices work fine without getting MAC explicitly

Thanks for the quick fix. Doesn't this fix though bring back the original race
that was fixed in commit 25266128fe16 ("virtio-net: fix race between set queues
and probe")? Or is being under the same rntl_lock session as register_netdev
enough to avoid the race?

Thanks,
Dragos