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

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Message-ID: <20250414200020.192715-1-jonas.gorski@gmail.com>
Date: Mon, 14 Apr 2025 22:00:20 +0200
From: Jonas Gorski <jonas.gorski@...il.com>
To: Nikolay Aleksandrov <razor@...ckwall.org>,
	Ido Schimmel <idosch@...dia.com>,
	"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>
Cc: bridge@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net v2] net: bridge: switchdev: do not notify new brentries as changed

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>
---
Changelog v1 -> v2:
- dropped the second patch always notifying dsa drivers on brentry changes
- dropped the cover letter, as its overkill for one patch and it mostly
  reiterated what is already written in here
- fixed the example in the commit message to use vlan_default_pvid 0
- fix thinko brake -> break
- extended the changelog to include the assurance that rtnetlink
  notifications should not be affected

 net/bridge/br_vlan.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
index d9a69ec9affe..939a3aa78d5c 100644
--- a/net/bridge/br_vlan.c
+++ b/net/bridge/br_vlan.c
@@ -715,8 +715,8 @@ static int br_vlan_add_existing(struct net_bridge *br,
 				u16 flags, bool *changed,
 				struct netlink_ext_ack *extack)
 {
-	bool would_change = __vlan_flags_would_change(vlan, flags);
 	bool becomes_brentry = false;
+	bool would_change = false;
 	int err;
 
 	if (!br_vlan_is_brentry(vlan)) {
@@ -725,6 +725,8 @@ static int br_vlan_add_existing(struct net_bridge *br,
 			return -EINVAL;
 
 		becomes_brentry = true;
+	} else {
+		would_change = __vlan_flags_would_change(vlan, flags);
 	}
 
 	/* Master VLANs that aren't brentries weren't notified before,
-- 
2.43.0