Re: [PATCH net] net: vlan: fix VLAN 0 refcount imbalance of toggling filtering during runtime

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 23 Jun 2025 19:30:08 +0800 Dong Chenchen wrote:
> $ ip link add bond0 type bond mode 0
> $ ip link add link bond0 name vlan0 type vlan id 0 protocol 802.1q
> $ ethtool -K bond0 rx-vlan-filter off
> $ ifconfig bond0 up
> $ ethtool -K bond0 rx-vlan-filter on
> $ ifconfig bond0 down
> $ ifconfig bond0 up
> $ ip link del vlan0

Please try to figure out the reasonable combinations in which we can
change the flags and bring the device up and down. Create a selftest
in bash and add it under tools/testing/selftests/net

> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
> index 06908e37c3d9..6e01ece0a95c 100644
> --- a/net/8021q/vlan.c
> +++ b/net/8021q/vlan.c
> @@ -504,12 +504,21 @@ static int vlan_device_event(struct notifier_block *unused, unsigned long event,
>  		break;
>  
>  	case NETDEV_CVLAN_FILTER_PUSH_INFO:
> +		flgs = dev_get_flags(dev);

Why call dev_get_flags()? You can test dev->flags & IFF_UP directly

> +		if (flgs & IFF_UP) {
> +			pr_info("adding VLAN 0 to HW filter on device %s\n",
> +				dev->name);
> +			vlan_vid_add(dev, htons(ETH_P_8021Q), 0);

Not sure if this works always, because if we have no vlan at all when
the device comes up vlan_info will be NULL and we won't even get here.

IIUC adding vlan 0 has to be handled early, where UP is handled.

> +		}
>  		err = vlan_filter_push_vids(vlan_info, htons(ETH_P_8021Q));
>  		if (err)
>  			return notifier_from_errno(err);
>  		break;
>  
>  	case NETDEV_CVLAN_FILTER_DROP_INFO:
> +		flgs = dev_get_flags(dev);
> +		if (flgs & IFF_UP)
> +			vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
>  		vlan_filter_drop_vids(vlan_info, htons(ETH_P_8021Q));
-- 
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