netdev - Re: [PATCHv2 net 2/2] team: reset team's flags when down link is P2P device

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Date: Tue, 18 Jul 2023 10:01:27 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
Cc: Jay Vosburgh <j.vosburgh@...il.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Eric Dumazet
 <edumazet@...gle.com>, Liang Li <liali@...hat.com>, Jiri Pirko
 <jiri@...dia.com>,  Nikolay Aleksandrov <razor@...ckwall.org>
Subject: Re: [PATCHv2 net 2/2] team: reset team's flags when down link is
 P2P device

Hi,

On Fri, 2023-07-14 at 16:13 +0800, Hangbin Liu wrote:
> When adding a point to point downlink to team device, we neglected to reset
> the team's flags, which were still using flags like BROADCAST and
> MULTICAST. Consequently, this would initiate ARP/DAD for P2P downlink
> interfaces, such as when adding a GRE device to team device.
> 
> Fix this by remove multicast/broadcast flags and add p2p and noarp flags.
> 
> Reported-by: Liang Li <liali@...hat.com>
> Links: https://bugzilla.redhat.com/show_bug.cgi?id=2221438
> Fixes: 1d76efe1577b ("team: add support for non-ethernet devices")
> Reviewed-by: Jiri Pirko <jiri@...dia.com>
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
>  drivers/net/team/team.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
> index 555b0b1e9a78..9104e373c8cb 100644
> --- a/drivers/net/team/team.c
> +++ b/drivers/net/team/team.c
> @@ -2135,6 +2135,11 @@ static void team_setup_by_port(struct net_device *dev,
>  	dev->mtu = port_dev->mtu;
>  	memcpy(dev->broadcast, port_dev->broadcast, port_dev->addr_len);
>  	eth_hw_addr_inherit(dev, port_dev);
> +
> +	if (port_dev->flags & IFF_POINTOPOINT) {
> +		dev->flags &= ~(IFF_BROADCAST | IFF_MULTICAST);
> +		dev->flags |= (IFF_POINTOPOINT | IFF_NOARP);
> +	}

It's unclear to me what happens with the following sequence of events:

* p2p dev is enslaved to team (IFF_BROADCAST cleared)
* p2p dev is removed from team
* plain ether device is enslaved to team.

I don't see where/when IFF_BROADCAST is set again. Could you please
point it out?

Thanks!

Paolo