Re: [PATCH v1 net-next 3/3] geneve: Support per-netns netdev unregistration.

[Paolo Abeni <pabeni@redhat.com>]

On 7/31/26 6:45 PM, Kuniyuki Iwashima wrote:
> geneve_exit_rtnl_net() iterates geneve devices whose sockets
> are in the dying netns and queues them for destruction.
> 
> So the devices may reside in different netns.
> 
> Let's use unregister_netdevice_queue_net() to support per-netns
> device unregistration.
> 
> list_del() is changed to list_del_init() to avoid queueing the
> same device twice.
> 
> Even after geneve_exit_rtnl_net() queues a cross-netns geneve
> device, geneve_dellink() can be called concurrently for it.
> In such a case, __rtnl_net_unlock() will perform the unregistration.
> 
> Note that geneve uses register_pernet_subsys() instead of _device(),
> so default_device_exit_batch() guarantees that the async per-netns
> works are flushed before ->exit().
> 
> Tested:
> 
> 1. Create geneve device across two netns.
> 
>   # ip netns add ns1
>   # ip netns add ns2
>   # ip -n ns1 link add geneve0 link-netns ns2 type geneve external
> 
> 2. Run bpftrace to check that geneve_uninit() is called between
>    ->exit_rtnl() and ->exit().
> 
>   # bpftrace -e '#include <linux/netdevice.h>
>   kprobe:geneve_uninit {
>       $dev = (struct net_device *)arg0;
>       printf("PID: %d | DEV: %s%s\n", pid, $dev->name, kstack());
>   }
>   kprobe:geneve_exit_rtnl_net,
>   kprobe:geneve_exit_net {
>       printf("PID: %d%s\n", pid, kstack());
>   }'
> 
> 3. Remove the netns where the geneve socket resides
> 
>   # ip netns del ns2
> 
> Now, we can see geneve0 is unregistered by per-netns work
> instead of cleanup_net() and it finishes before ->exit() to
> avoid WARN_ON_ONCE(!list_empty(&gn->sock_list)) there.
> 
>   PID: 571
>           geneve_exit_rtnl_net+5
>           ops_undo_list+702
>           cleanup_net+1122
>           process_scheduled_works+2538
>   ...
>   PID: 1047 | DEV: geneve0
>           geneve_uninit+5
>           unregister_netdevice_many_notify+7129
>           unregister_netdevice_many_net+1050
>           rtnl_net_work_func+136
>           process_scheduled_works+2538
>   ...
>   PID: 571
>           geneve_exit_net+5
>           ops_undo_list+1064
>           cleanup_net+1122
>           process_scheduled_works+2538
>   ...
> 
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---
>  drivers/net/geneve.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
> index f456a85dca77..a6a8978e3b81 100644
> --- a/drivers/net/geneve.c
> +++ b/drivers/net/geneve.c
> @@ -2502,12 +2502,13 @@ static int geneve_changelink(struct net_device *dev, struct nlattr *tb[],
>  	return err;
>  }
>  
> -static void __geneve_dellink(struct net_device *dev, struct list_head *head)
> +static void __geneve_dellink(struct net *net, struct net_device *dev,
> +			     struct list_head *head)
>  {
>  	struct geneve_dev *geneve = netdev_priv(dev);
>  
> -	list_del(&geneve->next);
> -	unregister_netdevice_queue(dev, head);
> +	list_del_init(&geneve->next);
> +	unregister_netdevice_queue_net(net, dev, head);
>  }
>  
>  static void geneve_dellink(struct net_device *dev, struct list_head *head)
> @@ -2518,7 +2519,8 @@ static void geneve_dellink(struct net_device *dev, struct list_head *head)
>  	gn = net_generic(geneve->net, geneve_net_id);
>  
>  	mutex_lock(&gn->lock);
> -	__geneve_dellink(dev, head);
> +	if (!list_empty(&geneve->next))
> +		__geneve_dellink(dev_net(dev), dev, head);

Sashiko noted that the lockdep chain between dev->lock, utn->loc and
gn->lock is not trivial, possibly a documentation follow-up would be useful

>  	mutex_unlock(&gn->lock);
>  }
>  
> @@ -2754,7 +2756,7 @@ static void __net_exit geneve_exit_rtnl_net(struct net *net,
>  	mutex_lock(&gn->lock);
>  
>  	list_for_each_entry_safe(geneve, next, &gn->geneve_list, next)
> -		__geneve_dellink(geneve->dev, dev_to_kill);
> +		__geneve_dellink(net, geneve->dev, dev_to_kill);

Here sashiko foresees some problem with CONFIG_DEBUG_NET_SMALL_RTNL
before full conversion to per netns lock even of ovs. Just more
follow-up, I guess.

/P

>  
>  	mutex_unlock(&gn->lock);
>  }