linux-kernel - Re: [PATCH net v2] net: bridge: switchdev: do not notify new brentries as changed

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Message-ID: <Z_455Kq1seP-KPhC@shredder>
Date: Tue, 15 Apr 2025 13:50:12 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Jonas Gorski <jonas.gorski@...il.com>
Cc: Nikolay Aleksandrov <razor@...ckwall.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Vladimir Oltean <vladimir.oltean@....com>, bridge@...ts.linux.dev,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: bridge: switchdev: do not notify new
 brentries as changed

On Mon, Apr 14, 2025 at 10:00:20PM +0200, Jonas Gorski wrote:
> When adding a bridge vlan that is pvid or untagged after the vlan has
> already been added to any other switchdev backed port, the vlan change
> will be propagated as changed, since the flags change.
> 
> This causes the vlan to not be added to the hardware for DSA switches,
> since the DSA handler ignores any vlans for the CPU or DSA ports that
> are changed.
> 
> E.g. the following order of operations would work:
> 
> $ ip link add swbridge type bridge vlan_filtering 1 vlan_default_pvid 0
> $ ip link set lan1 master swbridge
> $ bridge vlan add dev swbridge vid 1 pvid untagged self
> $ bridge vlan add dev lan1 vid 1 pvid untagged
> 
> but this order would break:
> 
> $ ip link add swbridge type bridge vlan_filtering 1 vlan_default_pvid 0
> $ ip link set lan1 master swbridge
> $ bridge vlan add dev lan1 vid 1 pvid untagged
> $ bridge vlan add dev swbridge vid 1 pvid untagged self
> 
> Additionally, the vlan on the bridge itself would become undeletable:
> 
> $ bridge vlan
> port              vlan-id
> lan1              1 PVID Egress Untagged
> swbridge          1 PVID Egress Untagged
> $ bridge vlan del dev swbridge vid 1 self
> $ bridge vlan
> port              vlan-id
> lan1              1 PVID Egress Untagged
> swbridge          1 Egress Untagged
> 
> since the vlan was never added to DSA's vlan list, so deleting it will
> cause an error, causing the bridge code to not remove it.
> 
> Fix this by checking if flags changed only for vlans that are already
> brentry and pass changed as false for those that become brentries, as
> these are a new vlan (member) from the switchdev point of view.
> 
> Since *changed is set to true for becomes_brentry = true regardless of
> would_change's value, this will not change any rtnetlink notification
> delivery, just the value passed on to switchdev in vlan->changed.
> 
> Fixes: 8d23a54f5bee ("net: bridge: switchdev: differentiate new VLANs from changed ones")
> Reviewed-by: Vladimir Oltean <vladimir.oltean@....com>
> Signed-off-by: Jonas Gorski <jonas.gorski@...il.com>

Reviewed-by: Ido Schimmel <idosch@...dia.com>