On 10 Dec 2025, at 13:59, Toke Høiland-Jørgensen wrote:
> 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 <[email protected]>
> Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
> ---
> net/openvswitch/vport-netdev.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/net/openvswitch/vport-netdev.c b/net/openvswitch/vport-netdev.c
> index 91a11067e458..519f038526f9 100644
> --- a/net/openvswitch/vport-netdev.c
> +++ b/net/openvswitch/vport-netdev.c
> @@ -160,10 +160,13 @@ 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();
> + if (netif_is_ovs_port(vport->dev)) {
Hi Toke,
Thanks for digging into this!
The patch looks technically correct to me, but maybe we should add a comment
here explaining why we can do it this way, i.e., why we can call
netif_is_ovs_port() without the lock.
For example:
/* We can avoid taking the rtnl lock as the IFF_OVS_DATAPATH flag is
set/cleared in either netdev_create()/netdev_destroy(), which are both called
under the global ovs_lock(). */
Additionally, I think the second netif_is_ovs_port() under the rtnl lock is not
required due to the above.
> + rtnl_lock();
> + /* check again while holding the lock */
> + if (netif_is_ovs_port(vport->dev))
> + ovs_netdev_detach_dev(vport);
> + rtnl_unlock();
> + }
>
> call_rcu(&vport->rcu, vport_netdev_free);
> }
> --
> 2.52.0
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