netdev - Re: [PATCH net-next] bonding: Remove support for use

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Message-ID: <92580e9d-55c1-4298-ae7a-00726a727fb5@blackwall.org>
Date: Tue, 17 Jun 2025 08:57:54 +0300
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Jay Vosburgh <jv@...sburgh.net>, netdev@...r.kernel.org
Cc: "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>,
 Jonathan Corbet <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>,
 Stanislav Fomichev <sdf@...ichev.me>, Hangbin Liu <liuhangbin@...il.com>,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

On 6/17/25 00:28, Jay Vosburgh wrote:
> 	 Remove the ability to disable use_carrier in bonding, and remove
> all code related to the old link state check that utilizes ethtool or
> ioctl to determine the link state of an interface in a bond.
> 
> 	To avoid acquiring RTNL many times per second, bonding's miimon
> link monitor inspects link state under RCU, but not under RTNL.  However,
> ethtool implementations in drivers may sleep, and therefore the ethtool or
> ioctl strategy is unsuitable for use with calls into driver ethtool
> functions.
> 
> 	The use_carrier option was introduced in 2003, to provide
> backwards compatibility for network device drivers that did not support
> the then-new netif_carrier_ok/on/off system.  Today, device drivers are
> expected to support netif_carrier_*, and the use_carrier backwards
> compatibility logic is no longer necessary.
> 
> 	Bonding now always behaves as if use_carrier=1, which relies on
> netif_carrier_ok() to determine the link state of interfaces.  This has
> been the default setting for use_carrier since its introduction.  For
> backwards compatibility, the option itself remains, but may only be set to
> 1, and queries will always return 1.
> 
> Reported-by: syzbot+b8c48ea38ca27d150063@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=b8c48ea38ca27d150063
> Link: https://lore.kernel.org/lkml/000000000000eb54bf061cfd666a@google.com/
> Link: https://lore.kernel.org/netdev/20240718122017.d2e33aaac43a.I10ab9c9ded97163aef4e4de10985cd8f7de60d28@changeid/
> Link: http://lore.kernel.org/netdev/aEt6LvBMwUMxmUyx@mini-arch
> Signed-off-by: Jay Vosburgh <jv@...sburgh.net>
> 
> ---
>  Documentation/networking/bonding.rst |  79 +++----------------
>  drivers/net/bonding/bond_main.c      | 113 ++-------------------------
>  drivers/net/bonding/bond_netlink.c   |  11 +--
>  drivers/net/bonding/bond_options.c   |   7 +-
>  drivers/net/bonding/bond_sysfs.c     |   6 +-
>  include/net/bonding.h                |   1 -
>  6 files changed, 25 insertions(+), 192 deletions(-)
> 
[snip]
> diff --git a/drivers/net/bonding/bond_netlink.c b/drivers/net/bonding/bond_netlink.c
> index ac5e402c34bc..98f9bef61474 100644
> --- a/drivers/net/bonding/bond_netlink.c
> +++ b/drivers/net/bonding/bond_netlink.c
> @@ -258,13 +258,8 @@ static int bond_changelink(struct net_device *bond_dev, struct nlattr *tb[],
>  			return err;
>  	}
>  	if (data[IFLA_BOND_USE_CARRIER]) {
> -		int use_carrier = nla_get_u8(data[IFLA_BOND_USE_CARRIER]);
> -
> -		bond_opt_initval(&newval, use_carrier);
> -		err = __bond_opt_set(bond, BOND_OPT_USE_CARRIER, &newval,
> -				     data[IFLA_BOND_USE_CARRIER], extack);
> -		if (err)
> -			return err;
> +		if (nla_get_u8(data[IFLA_BOND_USE_CARRIER]) != 1)

you can set extack to send back an error to the user that use_carrier
is now obsolete

> +			return -EINVAL;
>  	}
>  	if (data[IFLA_BOND_ARP_INTERVAL]) {
>  		int arp_interval = nla_get_u32(data[IFLA_BOND_ARP_INTERVAL]);
> @@ -676,7 +671,7 @@ static int bond_fill_info(struct sk_buff *skb,
>  			bond->params.peer_notif_delay * bond->params.miimon))
>  		goto nla_put_failure;
>  
> -	if (nla_put_u8(skb, IFLA_BOND_USE_CARRIER, bond->params.use_carrier))
> +	if (nla_put_u8(skb, IFLA_BOND_USE_CARRIER, 1))
>  		goto nla_put_failure;
>  
>  	if (nla_put_u32(skb, IFLA_BOND_ARP_INTERVAL, bond->params.arp_interval))