[PATCH net-next] bonding: Remove support for use_carrier = 0

[PATCH net-next] bonding: Remove support for use_carrier = 0

[Jay Vosburgh]

	 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@syzkaller.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@jvosburgh.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(-)

diff --git a/Documentation/networking/bonding.rst b/Documentation/networking/bonding.rst
index a4c1291d2561..4ee20f6ab733 100644
--- a/Documentation/networking/bonding.rst
+++ b/Documentation/networking/bonding.rst
@@ -576,10 +576,8 @@ 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
 
@@ -889,25 +887,14 @@ 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
 
@@ -2029,22 +2016,8 @@ 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
 ===============================
@@ -2128,34 +2101,6 @@ 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 c4d53e8e7c15..3534561fd932 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, "Obsolete, has no effect");
 module_param(mode, charp, 0);
 MODULE_PARM_DESC(mode, "Mode of operation; 0 for balance-rr, "
 		       "1 for active-backup, 2 for balance-xor, "
@@ -828,77 +827,6 @@ 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 */
@@ -1949,7 +1877,6 @@ 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 &&
@@ -1959,12 +1886,6 @@ 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,
@@ -2178,29 +2099,10 @@ 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,
@@ -2742,7 +2644,7 @@ 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:
@@ -6189,10 +6091,10 @@ 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) {
@@ -6439,7 +6341,6 @@ 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 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)
+			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))
diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
index 91893c29b899..98dbee2b6aba 100644
--- a/drivers/net/bonding/bond_options.c
+++ b/drivers/net/bonding/bond_options.c
@@ -185,7 +185,6 @@ 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}
 };
@@ -411,7 +410,7 @@ 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 = "Obsolete, has no effect",
 		.values = bond_use_carrier_tbl,
 		.set = bond_option_use_carrier_set
 	},
@@ -1068,10 +1067,6 @@ 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;
 }
 
diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
index 1e13bb170515..9a75ad3181ab 100644
--- a/drivers/net/bonding/bond_sysfs.c
+++ b/drivers/net/bonding/bond_sysfs.c
@@ -467,14 +467,12 @@ static ssize_t bonding_show_primary_reselect(struct device *d,
 static DEVICE_ATTR(primary_reselect, 0644,
 		   bonding_show_primary_reselect, bonding_sysfs_store_option);
 
-/* Show the use_carrier flag. */
+/* use_carrier is obsolete, but print value for compatibility */
 static ssize_t bonding_show_carrier(struct device *d,
 				    struct device_attribute *attr,
 				    char *buf)
 {
-	struct bonding *bond = to_bond(d);
-
-	return sysfs_emit(buf, "%d\n", bond->params.use_carrier);
+	return sysfs_emit(buf, "1\n");
 }
 static DEVICE_ATTR(use_carrier, 0644,
 		   bonding_show_carrier, bonding_sysfs_store_option);
diff --git a/include/net/bonding.h b/include/net/bonding.h
index 95f67b308c19..6fdf4d1e5256 100644
--- a/include/net/bonding.h
+++ b/include/net/bonding.h
@@ -124,7 +124,6 @@ struct bond_params {
 	int arp_interval;
 	int arp_validate;
 	int arp_all_targets;
-	int use_carrier;
 	int fail_over_mac;
 	int updelay;
 	int downdelay;
-- 
2.25.1

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Stanislav Fomichev]

On 06/16, 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@syzkaller.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@jvosburgh.net>

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

Maybe better to target 'net' with the following?
Fixes: f7a11cba0ed7 ("bonding: hold ops lock around get_link")

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Jay Vosburgh]

Stanislav Fomichev <stfomichev@gmail.com> wrote:

>On 06/16, 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@syzkaller.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@jvosburgh.net>
>
>Acked-by: Stanislav Fomichev <sdf@fomichev.me>
>
>Maybe better to target 'net' with the following?
>Fixes: f7a11cba0ed7 ("bonding: hold ops lock around get_link")

	I targeted net-next and left the Fixes: tag off on purpose.

	First, the bug this nominally fixes is many years old, and
wasn't introduced by f7a11cba0ed7.

	More importantly, though, this patch is removing functionality
that someone theoretically could be relying on, and I don't think such
removals should happen in the middle of a stable series.  The default
setting for use_carrier (i.e., using netif_carrier) will never hit the
issue in practice, so the exposure seems to be minimal for common use.

	-J

---
	-Jay Vosburgh, jv@jvosburgh.net

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Nikolay Aleksandrov]

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@syzkaller.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@jvosburgh.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))

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Tonghao Zhang]

> 2025年6月17日 05:28，Jay Vosburgh <jv@jvosburgh.net> 写道：
> 
> 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@syzkaller.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@jvosburgh.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(-)
> 
> diff --git a/Documentation/networking/bonding.rst b/Documentation/networking/bonding.rst
> index a4c1291d2561..4ee20f6ab733 100644
> --- a/Documentation/networking/bonding.rst
> +++ b/Documentation/networking/bonding.rst
> @@ -576,10 +576,8 @@ 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
> 
> @@ -889,25 +887,14 @@ 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
> 
> @@ -2029,22 +2016,8 @@ 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
> ===============================
> @@ -2128,34 +2101,6 @@ 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 c4d53e8e7c15..3534561fd932 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, "Obsolete, has no effect");
> module_param(mode, charp, 0);
> MODULE_PARM_DESC(mode, "Mode of operation; 0 for balance-rr, "
>       "1 for active-backup, 2 for balance-xor, "
> @@ -828,77 +827,6 @@ 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 */
> @@ -1949,7 +1877,6 @@ 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 &&
> @@ -1959,12 +1886,6 @@ 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,
> @@ -2178,29 +2099,10 @@ 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,
> @@ -2742,7 +2644,7 @@ 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:
> @@ -6189,10 +6091,10 @@ 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) {
> @@ -6439,7 +6341,6 @@ 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 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)
> + 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))
> diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
> index 91893c29b899..98dbee2b6aba 100644
> --- a/drivers/net/bonding/bond_options.c
> +++ b/drivers/net/bonding/bond_options.c
> @@ -185,7 +185,6 @@ 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}
> };
Your other patch deletes these lines.
> @@ -411,7 +410,7 @@ 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 = "Obsolete, has no effect”,
Add more information? "Obsolete, option has no effect, netif_carrier_ok used as default"
> 
> .values = bond_use_carrier_tbl,
> .set = bond_option_use_carrier_set
> },
> @@ -1068,10 +1067,6 @@ 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;
> }
> 
> diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
> index 1e13bb170515..9a75ad3181ab 100644
> --- a/drivers/net/bonding/bond_sysfs.c
> +++ b/drivers/net/bonding/bond_sysfs.c
> @@ -467,14 +467,12 @@ static ssize_t bonding_show_primary_reselect(struct device *d,
> static DEVICE_ATTR(primary_reselect, 0644,
>   bonding_show_primary_reselect, bonding_sysfs_store_option);
> 
> -/* Show the use_carrier flag. */
> +/* use_carrier is obsolete, but print value for compatibility */
> static ssize_t bonding_show_carrier(struct device *d,
>    struct device_attribute *attr,
>    char *buf)
> {
> - struct bonding *bond = to_bond(d);
> -
> - return sysfs_emit(buf, "%d\n", bond->params.use_carrier);
> + return sysfs_emit(buf, "1\n");
> }
> static DEVICE_ATTR(use_carrier, 0644,
>   bonding_show_carrier, bonding_sysfs_store_option);
> diff --git a/include/net/bonding.h b/include/net/bonding.h
> index 95f67b308c19..6fdf4d1e5256 100644
> --- a/include/net/bonding.h
> +++ b/include/net/bonding.h
> @@ -124,7 +124,6 @@ struct bond_params {
> int arp_interval;
> int arp_validate;
> int arp_all_targets;
> - int use_carrier;
> int fail_over_mac;
> int updelay;
> int downdelay;
> -- 
> 2.25.1
> 
> 
> 

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Stanislav Fomichev]

On 06/16, Jay Vosburgh wrote:
> Stanislav Fomichev <stfomichev@gmail.com> wrote:
> 
> >On 06/16, 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@syzkaller.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@jvosburgh.net>
> >
> >Acked-by: Stanislav Fomichev <sdf@fomichev.me>
> >
> >Maybe better to target 'net' with the following?
> >Fixes: f7a11cba0ed7 ("bonding: hold ops lock around get_link")
> 
> 	I targeted net-next and left the Fixes: tag off on purpose.
> 
> 	First, the bug this nominally fixes is many years old, and
> wasn't introduced by f7a11cba0ed7.
> 
> 	More importantly, though, this patch is removing functionality
> that someone theoretically could be relying on, and I don't think such
> removals should happen in the middle of a stable series.  The default
> setting for use_carrier (i.e., using netif_carrier) will never hit the
> issue in practice, so the exposure seems to be minimal for common use.

SG, especially assuming that use_carrier has a default of 1 (so the
issue should not appear in most/default setups).

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Jay Vosburgh]

Nikolay Aleksandrov <razor@blackwall.org> wrote:

>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@syzkaller.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@jvosburgh.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

	Fair point, will add that and repost.

	-J

>> +			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))

---
	-Jay Vosburgh, jv@jvosburgh.net

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Jay Vosburgh]

Tonghao Zhang <tonghao@bamaicloud.com> wrote:

>> 2025年6月17日 05:28，Jay Vosburgh <jv@jvosburgh.net> 写道：
>> 
>> 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@syzkaller.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@jvosburgh.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(-)
>> 
>> diff --git a/Documentation/networking/bonding.rst b/Documentation/networking/bonding.rst
>> index a4c1291d2561..4ee20f6ab733 100644
>> --- a/Documentation/networking/bonding.rst
>> +++ b/Documentation/networking/bonding.rst
>> @@ -576,10 +576,8 @@ 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
>> 
>> @@ -889,25 +887,14 @@ 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
>> 
>> @@ -2029,22 +2016,8 @@ 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
>> ===============================
>> @@ -2128,34 +2101,6 @@ 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 c4d53e8e7c15..3534561fd932 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, "Obsolete, has no effect");
>> module_param(mode, charp, 0);
>> MODULE_PARM_DESC(mode, "Mode of operation; 0 for balance-rr, "
>>       "1 for active-backup, 2 for balance-xor, "
>> @@ -828,77 +827,6 @@ 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 */
>> @@ -1949,7 +1877,6 @@ 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 &&
>> @@ -1959,12 +1886,6 @@ 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,
>> @@ -2178,29 +2099,10 @@ 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,
>> @@ -2742,7 +2644,7 @@ 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:
>> @@ -6189,10 +6091,10 @@ 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) {
>> @@ -6439,7 +6341,6 @@ 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 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)
>> + 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))
>> diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
>> index 91893c29b899..98dbee2b6aba 100644
>> --- a/drivers/net/bonding/bond_options.c
>> +++ b/drivers/net/bonding/bond_options.c
>> @@ -185,7 +185,6 @@ 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}
>> };

>Your other patch deletes these lines.

	Correct.  The initial version of the patch would silently ignore
setting use_carrier off.  I changed it so that users that actually
disable the option would receive an error.  This should make it clear
that the functionality they're trying to use does not exist.

>> @@ -411,7 +410,7 @@ 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 = "Obsolete, has no effect”,

>Add more information? "Obsolete, option has no effect, netif_carrier_ok used as default"

	Will do.

	-J

>> .values = bond_use_carrier_tbl,
>> .set = bond_option_use_carrier_set
>> },
>> @@ -1068,10 +1067,6 @@ 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;
>> }
>> 
>> diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
>> index 1e13bb170515..9a75ad3181ab 100644
>> --- a/drivers/net/bonding/bond_sysfs.c
>> +++ b/drivers/net/bonding/bond_sysfs.c
>> @@ -467,14 +467,12 @@ static ssize_t bonding_show_primary_reselect(struct device *d,
>> static DEVICE_ATTR(primary_reselect, 0644,
>>   bonding_show_primary_reselect, bonding_sysfs_store_option);
>> 
>> -/* Show the use_carrier flag. */
>> +/* use_carrier is obsolete, but print value for compatibility */
>> static ssize_t bonding_show_carrier(struct device *d,
>>    struct device_attribute *attr,
>>    char *buf)
>> {
>> - struct bonding *bond = to_bond(d);
>> -
>> - return sysfs_emit(buf, "%d\n", bond->params.use_carrier);
>> + return sysfs_emit(buf, "1\n");
>> }
>> static DEVICE_ATTR(use_carrier, 0644,
>>   bonding_show_carrier, bonding_sysfs_store_option);
>> diff --git a/include/net/bonding.h b/include/net/bonding.h
>> index 95f67b308c19..6fdf4d1e5256 100644
>> --- a/include/net/bonding.h
>> +++ b/include/net/bonding.h
>> @@ -124,7 +124,6 @@ struct bond_params {
>> int arp_interval;
>> int arp_validate;
>> int arp_all_targets;
>> - int use_carrier;
>> int fail_over_mac;
>> int updelay;
>> int downdelay;
>> -- 
>> 2.25.1

---
	-Jay Vosburgh, jv@jvosburgh.net

Re: [PATCH net-next] bonding: Remove support for use_carrier = 0

[Stanislav Fomichev]

On 06/16, 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@syzkaller.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@jvosburgh.net>

Hey Jay, are you planning to send a v2 for this? The syzkaller is still
complaining :-(

https://lore.kernel.org/netdev/688e282f.050a0220.81582.0000.GAE@google.com/