netdev - [PATCH v2] net: openvswitch: Avoid needlessly taking the RTNL on vport destroy

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Message-ID: <20251211115006.228876-1-toke@redhat.com>
Date: Thu, 11 Dec 2025 12:50:05 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Aaron Conole <aconole@...hat.com>,
	Eelco Chaudron <echaudro@...hat.com>,
	Ilya Maximets <i.maximets@....org>,
	Alexei Starovoitov <ast@...nel.org>,
	Jesse Gross <jesse@...ira.com>
Cc: Toke Høiland-Jørgensen <toke@...hat.com>,
	Adrian Moreno <amorenoz@...hat.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>,
	netdev@...r.kernel.org,
	dev@...nvswitch.org
Subject: [PATCH v2] net: openvswitch: Avoid needlessly taking the RTNL on vport destroy

The openvswitch teardown code will immediately call
ovs_netdev_detach_dev() in response to a NETDEV_UNREGISTER notification.
It will then start the dp_notify_work workqueue, which will later end up
calling the vport destroy() callback. This callback takes the RTNL to do
another ovs_netdev_detach_port(), which in this case is unnecessary.
This causes extra pressure on the RTNL, in some cases leading to
"unregister_netdevice: waiting for XX to become free" warnings on
teardown.

We can straight-forwardly avoid the extra RTNL lock acquisition by
checking the device flags before taking the lock, and skip the locking
altogether if the IFF_OVS_DATAPATH flag has already been unset.

Fixes: b07c26511e94 ("openvswitch: fix vport-netdev unregister")
Tested-by: Adrian Moreno <amorenoz@...hat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
v2:
- Expand comments explaining the logic

 net/openvswitch/vport-netdev.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/net/openvswitch/vport-netdev.c b/net/openvswitch/vport-netdev.c
index 91a11067e458..6574f9bcdc02 100644
--- a/net/openvswitch/vport-netdev.c
+++ b/net/openvswitch/vport-netdev.c
@@ -160,10 +160,19 @@ void ovs_netdev_detach_dev(struct vport *vport)
 
 static void netdev_destroy(struct vport *vport)
 {
-	rtnl_lock();
-	if (netif_is_ovs_port(vport->dev))
-		ovs_netdev_detach_dev(vport);
-	rtnl_unlock();
+	/* When called from ovs_db_notify_wq() after a dp_device_event(), the
+	 * port has already been detached, so we can avoid taking the RTNL by
+	 * checking this first.
+	 */
+	if (netif_is_ovs_port(vport->dev)) {
+		rtnl_lock();
+		/* Check again while holding the lock to ensure we don't race
+		 * with the netdev notifier and detach twice.
+		 */
+		if (netif_is_ovs_port(vport->dev))
+			ovs_netdev_detach_dev(vport);
+		rtnl_unlock();
+	}
 
 	call_rcu(&vport->rcu, vport_netdev_free);
 }
-- 
2.52.0