linux-kernel - Re: [PATCH net] net: dsa: fix VLAN 0 filter imbalance when toggling filtering

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Message-ID: <cf0d5622-9b35-4a33-8680-2501d61f3cdf@redhat.com>
Date: Thu, 24 Apr 2025 11:15:41 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jonas Gorski <jonas.gorski@...il.com>, Andrew Lunn <andrew@...n.ch>,
 Vladimir Oltean <olteanv@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>,
 Florian Fainelli <f.fainelli@...il.com>
Cc: Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: fix VLAN 0 filter imbalance when toggling
 filtering

On 4/22/25 8:49 PM, Jonas Gorski wrote:
> When a net device has NETIF_F_HW_VLAN_CTAG_FILTER set, the 8021q code
> will add VLAN 0 when enabling the device, and remove it on disabling it
> again.
> 
> But since we are changing NETIF_F_HW_VLAN_CTAG_FILTER during runtime in
> dsa_user_manage_vlan_filtering(), user ports that are already enabled
> may end up with no VLAN 0 configured, or VLAN 0 left configured.

Why this is a problem specifically for dsa and not a generic one? others
devices allow flipping the NETIF_F_HW_VLAN_CTAG_FILTER feature at runtime.

AFAICS dsa_user_manage_vlan_filtering() is currently missing a call to
netdev_update_features(), why is that not sufficient nor necessary?

Thanks,

Paolo