Message-ID: <aLcXNO6ginmuiBOw@mini-arch>
Date: Tue, 2 Sep 2025 09:11:32 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Jay Vosburgh <jv@...sburgh.net>
Cc: netdev@...r.kernel.org, "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>, linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next] bonding: Remove support for use_carrier

On 08/29, Jay Vosburgh wrote:
> 	 Remove the implementation of use_carrier, the link monitoring
> method that utilizes ethtool or ioctl to determine the link state of an
> interface in a bond.  Bonding will always behaves as if use_carrier=1,
> which relies on netif_carrier_ok() to determine the link state of
> interfaces.
> 
> 	To avoid acquiring RTNL many times per second, bonding inspects
> link state under RCU, but not under RTNL.  However, ethtool
> implementations in drivers may sleep, and therefore this 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.  Device drivers are now
> expected to support netif_carrier_*, and the use_carrier backwards
> compatibility logic is no longer necessary.
> 
> 	The option itself remains, but when queried always returns 1,
> and may only be set to 1.
> 
> Link: https://lore.kernel.org/lkml/000000000000eb54bf061cfd666a@google.com/
> Link: https://lore.kernel.org/netdev/20240718122017.d2e33aaac43a.I10ab9c9ded97163aef4e4de10985cd8f7de60d28@changeid/
> Signed-off-by: Jay Vosburgh <jv@...sburgh.net>
> 
> ---
> 
> Note: Deliberately omitting a Fixes tag to avoid removing functionality
> in older kernels that may be in use.

What about syzbot metadata?

Reported-by: syzbot+b8c48ea38ca27d150063@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b8c48ea38ca27d150063

?

>  Documentation/networking/bonding.rst |  79 +++----------------
>  drivers/net/bonding/bond_main.c      | 113 ++-------------------------
>  drivers/net/bonding/bond_netlink.c   |  14 ++--
>  drivers/net/bonding/bond_options.c   |   7 +-
>  drivers/net/bonding/bond_sysfs.c     |   6 +-
>  include/net/bonding.h                |   1 -
>  6 files changed, 28 insertions(+), 192 deletions(-)
> 
> diff --git a/Documentation/networking/bonding.rst b/Documentation/networking/bonding.rst
> index f8f5766703d4..a2b42ae719d2 100644
> --- a/Documentation/networking/bonding.rst
> +++ b/Documentation/networking/bonding.rst
> @@ -582,10 +582,8 @@ miimon
>  	This determines how often the link state of each slave is
>  	inspected for link failures.  A value of zero disables MII
>  	link monitoring.  A value of 100 is a good starting point.
> -	The use_carrier option, below, affects how the link state is
> -	determined.  See the High Availability section for additional
> -	information.  The default value is 100 if arp_interval is not
> -	set.
> +
> +	The default value is 100 if arp_interval is not set.
>  
>  min_links
>  
> @@ -896,25 +894,14 @@ updelay
>  
>  use_carrier
>  
> -	Specifies whether or not miimon should use MII or ETHTOOL
> -	ioctls vs. netif_carrier_ok() to determine the link
> -	status. The MII or ETHTOOL ioctls are less efficient and
> -	utilize a deprecated calling sequence within the kernel.  The
> -	netif_carrier_ok() relies on the device driver to maintain its
> -	state with netif_carrier_on/off; at this writing, most, but
> -	not all, device drivers support this facility.
> -
> -	If bonding insists that the link is up when it should not be,
> -	it may be that your network device driver does not support
> -	netif_carrier_on/off.  The default state for netif_carrier is
> -	"carrier on," so if a driver does not support netif_carrier,
> -	it will appear as if the link is always up.  In this case,
> -	setting use_carrier to 0 will cause bonding to revert to the
> -	MII / ETHTOOL ioctl method to determine the link state.
> -
> -	A value of 1 enables the use of netif_carrier_ok(), a value of
> -	0 will use the deprecated MII / ETHTOOL ioctls.  The default
> -	value is 1.
> +	Obsolete option that previously selected between MII /
> +	ETHTOOL ioctls and netif_carrier_ok() to determine link
> +	state.
> +
> +	All link state checks are now done with netif_carrier_ok().
> +
> +	For backwards compatibility, this option's value may be inspected
> +	or set.  The only valid setting is 1.
>  
>  xmit_hash_policy
>  
> @@ -2036,22 +2023,8 @@ depending upon the device driver to maintain its carrier state, by
>  querying the device's MII registers, or by making an ethtool query to
>  the device.
>  
> -If the use_carrier module parameter is 1 (the default value),
> -then the MII monitor will rely on the driver for carrier state
> -information (via the netif_carrier subsystem).  As explained in the
> -use_carrier parameter information, above, if the MII monitor fails to
> -detect carrier loss on the device (e.g., when the cable is physically
> -disconnected), it may be that the driver does not support
> -netif_carrier.
> -
> -If use_carrier is 0, then the MII monitor will first query the
> -device's (via ioctl) MII registers and check the link state.  If that
> -request fails (not just that it returns carrier down), then the MII
> -monitor will make an ethtool ETHTOOL_GLINK request to attempt to obtain
> -the same information.  If both methods fail (i.e., the driver either
> -does not support or had some error in processing both the MII register
> -and ethtool requests), then the MII monitor will assume the link is
> -up.
> +The MII monitor relies on the driver for carrier state information (via
> +the netif_carrier subsystem).
>  
>  8. Potential Sources of Trouble
>  ===============================
> @@ -2135,34 +2108,6 @@ This will load tg3 and e1000 modules before loading the bonding one.
>  Full documentation on this can be found in the modprobe.d and modprobe
>  manual pages.
>  
> -8.3. Painfully Slow Or No Failed Link Detection By Miimon
> ----------------------------------------------------------
> -
> -By default, bonding enables the use_carrier option, which
> -instructs bonding to trust the driver to maintain carrier state.
> -
> -As discussed in the options section, above, some drivers do
> -not support the netif_carrier_on/_off link state tracking system.
> -With use_carrier enabled, bonding will always see these links as up,
> -regardless of their actual state.
> -
> -Additionally, other drivers do support netif_carrier, but do
> -not maintain it in real time, e.g., only polling the link state at
> -some fixed interval.  In this case, miimon will detect failures, but
> -only after some long period of time has expired.  If it appears that
> -miimon is very slow in detecting link failures, try specifying
> -use_carrier=0 to see if that improves the failure detection time.  If
> -it does, then it may be that the driver checks the carrier state at a
> -fixed interval, but does not cache the MII register values (so the
> -use_carrier=0 method of querying the registers directly works).  If
> -use_carrier=0 does not improve the failover, then the driver may cache
> -the registers, or the problem may be elsewhere.
> -
> -Also, remember that miimon only checks for the device's
> -carrier state.  It has no way to determine the state of devices on or
> -beyond other ports of a switch, or if a switch is refusing to pass
> -traffic while still maintaining carrier on.
> -
>  9. SNMP agents
>  ===============
>  
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 257333c88710..f25c2d2c9181 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -142,8 +142,7 @@ module_param(downdelay, int, 0);
>  MODULE_PARM_DESC(downdelay, "Delay before considering link down, "
>  			    "in milliseconds");
>  module_param(use_carrier, int, 0);
> -MODULE_PARM_DESC(use_carrier, "Use netif_carrier_ok (vs MII ioctls) in miimon; "
> -			      "0 for off, 1 for on (default)");
> +MODULE_PARM_DESC(use_carrier, "option obsolete, use_carrier cannot be disabled");
>  module_param(mode, charp, 0);
>  MODULE_PARM_DESC(mode, "Mode of operation; 0 for balance-rr, "
>  		       "1 for active-backup, 2 for balance-xor, "
> @@ -830,77 +829,6 @@ const char *bond_slave_link_status(s8 link)
>  	}
>  }
>  
> -/* if <dev> supports MII link status reporting, check its link status.
> - *
> - * We either do MII/ETHTOOL ioctls, or check netif_carrier_ok(),
> - * depending upon the setting of the use_carrier parameter.
> - *
> - * Return either BMSR_LSTATUS, meaning that the link is up (or we
> - * can't tell and just pretend it is), or 0, meaning that the link is
> - * down.
> - *
> - * If reporting is non-zero, instead of faking link up, return -1 if
> - * both ETHTOOL and MII ioctls fail (meaning the device does not
> - * support them).  If use_carrier is set, return whatever it says.
> - * It'd be nice if there was a good way to tell if a driver supports
> - * netif_carrier, but there really isn't.
> - */
> -static int bond_check_dev_link(struct bonding *bond,
> -			       struct net_device *slave_dev, int reporting)
> -{
> -	const struct net_device_ops *slave_ops = slave_dev->netdev_ops;
> -	struct mii_ioctl_data *mii;
> -	struct ifreq ifr;
> -	int ret;
> -
> -	if (!reporting && !netif_running(slave_dev))
> -		return 0;
> -
> -	if (bond->params.use_carrier)
> -		return netif_carrier_ok(slave_dev) ? BMSR_LSTATUS : 0;
> -
> -	/* Try to get link status using Ethtool first. */
> -	if (slave_dev->ethtool_ops->get_link) {
> -		netdev_lock_ops(slave_dev);
> -		ret = slave_dev->ethtool_ops->get_link(slave_dev);
> -		netdev_unlock_ops(slave_dev);
> -
> -		return ret ? BMSR_LSTATUS : 0;
> -	}
> -
> -	/* Ethtool can't be used, fallback to MII ioctls. */
> -	if (slave_ops->ndo_eth_ioctl) {
> -		/* TODO: set pointer to correct ioctl on a per team member
> -		 *       bases to make this more efficient. that is, once
> -		 *       we determine the correct ioctl, we will always
> -		 *       call it and not the others for that team
> -		 *       member.
> -		 */
> -
> -		/* We cannot assume that SIOCGMIIPHY will also read a
> -		 * register; not all network drivers (e.g., e100)
> -		 * support that.
> -		 */
> -
> -		/* Yes, the mii is overlaid on the ifreq.ifr_ifru */
> -		strscpy_pad(ifr.ifr_name, slave_dev->name, IFNAMSIZ);
> -		mii = if_mii(&ifr);
> -
> -		if (dev_eth_ioctl(slave_dev, &ifr, SIOCGMIIPHY) == 0) {
> -			mii->reg_num = MII_BMSR;
> -			if (dev_eth_ioctl(slave_dev, &ifr, SIOCGMIIREG) == 0)
> -				return mii->val_out & BMSR_LSTATUS;
> -		}
> -	}
> -
> -	/* If reporting, report that either there's no ndo_eth_ioctl,
> -	 * or both SIOCGMIIREG and get_link failed (meaning that we
> -	 * cannot report link status).  If not reporting, pretend
> -	 * we're ok.
> -	 */
> -	return reporting ? -1 : BMSR_LSTATUS;
> -}
> -
>  /*----------------------------- Multicast list ------------------------------*/
>  
>  /* Push the promiscuity flag down to appropriate slaves */
> @@ -1966,7 +1894,6 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
>  	const struct net_device_ops *slave_ops = slave_dev->netdev_ops;
>  	struct slave *new_slave = NULL, *prev_slave;
>  	struct sockaddr_storage ss;
> -	int link_reporting;
>  	int res = 0, i;
>  
>  	if (slave_dev->flags & IFF_MASTER &&
> @@ -1976,12 +1903,6 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
>  		return -EPERM;
>  	}
>  
> -	if (!bond->params.use_carrier &&
> -	    slave_dev->ethtool_ops->get_link == NULL &&
> -	    slave_ops->ndo_eth_ioctl == NULL) {
> -		slave_warn(bond_dev, slave_dev, "no link monitoring support\n");
> -	}
> -
>  	/* already in-use? */
>  	if (netdev_is_rx_handler_busy(slave_dev)) {
>  		SLAVE_NL_ERR(bond_dev, slave_dev, extack,
> @@ -2195,29 +2116,10 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
>  
>  	new_slave->last_tx = new_slave->last_rx;
>  
> -	if (bond->params.miimon && !bond->params.use_carrier) {
> -		link_reporting = bond_check_dev_link(bond, slave_dev, 1);
> -
> -		if ((link_reporting == -1) && !bond->params.arp_interval) {
> -			/* miimon is set but a bonded network driver
> -			 * does not support ETHTOOL/MII and
> -			 * arp_interval is not set.  Note: if
> -			 * use_carrier is enabled, we will never go
> -			 * here (because netif_carrier is always
> -			 * supported); thus, we don't need to change
> -			 * the messages for netif_carrier.
> -			 */
> -			slave_warn(bond_dev, slave_dev, "MII and ETHTOOL support not available for slave, and arp_interval/arp_ip_target module parameters not specified, thus bonding will not detect link failures! see bonding.txt for details\n");
> -		} else if (link_reporting == -1) {
> -			/* unable get link status using mii/ethtool */
> -			slave_warn(bond_dev, slave_dev, "can't get link status from slave; the network driver associated with this interface does not support MII or ETHTOOL link status reporting, thus miimon has no effect on this interface\n");
> -		}
> -	}
> -
>  	/* check for initial state */
>  	new_slave->link = BOND_LINK_NOCHANGE;
>  	if (bond->params.miimon) {
> -		if (bond_check_dev_link(bond, slave_dev, 0) == BMSR_LSTATUS) {
> +		if (netif_carrier_ok(slave_dev)) {
>  			if (bond->params.updelay) {
>  				bond_set_slave_link_state(new_slave,
>  							  BOND_LINK_BACK,
> @@ -2759,7 +2661,7 @@ static int bond_miimon_inspect(struct bonding *bond)
>  	bond_for_each_slave_rcu(bond, slave, iter) {
>  		bond_propose_link_state(slave, BOND_LINK_NOCHANGE);
>  
> -		link_state = bond_check_dev_link(bond, slave->dev, 0);
> +		link_state = netif_carrier_ok(slave->dev);
>  
>  		switch (slave->link) {
>  		case BOND_LINK_UP:
> @@ -6257,10 +6159,10 @@ static int __init bond_check_params(struct bond_params *params)
>  		downdelay = 0;
>  	}
>  
> -	if ((use_carrier != 0) && (use_carrier != 1)) {
> -		pr_warn("Warning: use_carrier module parameter (%d), not of valid value (0/1), so it was set to 1\n",
> -			use_carrier);
> -		use_carrier = 1;
> +	if (use_carrier != 1) {
> +		pr_err("Error: invalid use_carrier parameter (%d)\n",
> +		       use_carrier);
> +		return -EINVAL;
>  	}
>  
>  	if (num_peer_notif < 0 || num_peer_notif > 255) {
> @@ -6507,7 +6409,6 @@ static int __init bond_check_params(struct bond_params *params)
>  	params->updelay = updelay;
>  	params->downdelay = downdelay;
>  	params->peer_notif_delay = 0;
> -	params->use_carrier = use_carrier;
>  	params->lacp_active = 1;
>  	params->lacp_fast = lacp_fast;
>  	params->primary[0] = 0;
> diff --git a/drivers/net/bonding/bond_netlink.c b/drivers/net/bonding/bond_netlink.c
> index 57fff2421f1b..e573b34a1bbc 100644
> --- a/drivers/net/bonding/bond_netlink.c
> +++ b/drivers/net/bonding/bond_netlink.c
> @@ -259,13 +259,11 @@ 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) {
> +			NL_SET_ERR_MSG_ATTR(extack, data[IFLA_BOND_USE_CARRIER],
> +					    "option obsolete, use_carrier cannot be disabled");
> +			return -EINVAL;
> +		}
>  	}
>  	if (data[IFLA_BOND_ARP_INTERVAL]) {
>  		int arp_interval = nla_get_u32(data[IFLA_BOND_ARP_INTERVAL]);
> @@ -688,7 +686,7 @@ 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))
> diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
> index 3b6f815c55ff..c0a5eb8766b5 100644
> --- a/drivers/net/bonding/bond_options.c
> +++ b/drivers/net/bonding/bond_options.c
> @@ -187,7 +187,6 @@ static const struct bond_opt_value bond_primary_reselect_tbl[] = {
>  };
>  
>  static const struct bond_opt_value bond_use_carrier_tbl[] = {
> -	{ "off", 0,  0},
>  	{ "on",  1,  BOND_VALFLAG_DEFAULT},
>  	{ NULL,  -1, 0}
>  };
> @@ -419,7 +418,7 @@ static const struct bond_option bond_opts[BOND_OPT_LAST] = {
>  	[BOND_OPT_USE_CARRIER] = {
>  		.id = BOND_OPT_USE_CARRIER,
>  		.name = "use_carrier",
> -		.desc = "Use netif_carrier_ok (vs MII ioctls) in miimon",
> +		.desc = "option obsolete, use_carrier cannot be disabled",
>  		.values = bond_use_carrier_tbl,
>  		.set = bond_option_use_carrier_set
>  	},
> @@ -1091,10 +1090,6 @@ static int bond_option_peer_notif_delay_set(struct bonding *bond,
>  static int bond_option_use_carrier_set(struct bonding *bond,
>  				       const struct bond_opt_value *newval)
>  {
> -	netdev_dbg(bond->dev, "Setting use_carrier to %llu\n",
> -		   newval->value);
> -	bond->params.use_carrier = newval->value;
> -
>  	return 0;

Acked-by: Stanislav Fomichev <sdf@...ichev.me>

nit: any reason not to return -EINVAL here when the new value is not "1"?
You do it for the module param, but not for the sysfs file here.

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