Subject: Re: [PATCH v2 net] bonding: only set speed/duplex to unknown, if getting speed failed

From: Jay Vosburgh <[email-masked]>
Date: Tue, 03 Feb 2026 10:34:48 -0800

Thomas Bogendoerfer <[email-masked]> wrote:

>bond_update_speed_duplex() first set speed/duplex to unknown and
>then asks slave driver for current speed/duplex. Since getting
>speed/duplex might take longer there is a race, where this false state
>is visible by /proc/net/bonding. With commit 691b2bf14946 ("bonding:
> update port speed when getting bond speed") this race gets more visible,
>if user space is calling ethtool on a regular base.
>
>Fix this by only setting speed/duplex to unknown, if link speed is
>really unknown/unusable.
>
>Fixes: 98f41f694f46 ("bonding:update speed/duplex for NETDEV_CHANGE")
>Signed-off-by: Thomas Bogendoerfer <[email-masked]>

Acked-by: Jay Vosburgh <[email-masked]>

	I think this Fixes tag is fine, it's far enough back in time to
be effectively all stable releases.  The actual change in the patch is
obviously correct, as well.

	-J

>---
>v2: corrected fixes tag
>v1: https://lore.kernel.org/all/[email-masked]/
>
> drivers/net/bonding/bond_main.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index e7caf400a59c..4cdf89b21ca0 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -791,26 +791,29 @@ static int bond_update_speed_duplex(struct slave *slave)
> 	struct ethtool_link_ksettings ecmd;
> 	int res;
> 
>-	slave->speed = SPEED_UNKNOWN;
>-	slave->duplex = DUPLEX_UNKNOWN;
>-
> 	res = __ethtool_get_link_ksettings(slave_dev, &ecmd);
> 	if (res < 0)
>-		return 1;
>+		goto speed_duplex_unknown;
> 	if (ecmd.base.speed == 0 || ecmd.base.speed == ((__u32)-1))
>-		return 1;
>+		goto speed_duplex_unknown;
> 	switch (ecmd.base.duplex) {
> 	case DUPLEX_FULL:
> 	case DUPLEX_HALF:
> 		break;
> 	default:
>-		return 1;
>+		goto speed_duplex_unknown;
> 	}
> 
> 	slave->speed = ecmd.base.speed;
> 	slave->duplex = ecmd.base.duplex;
> 
> 	return 0;
>+
>+speed_duplex_unknown:
>+	slave->speed = SPEED_UNKNOWN;
>+	slave->duplex = DUPLEX_UNKNOWN;
>+
>+	return 1;
> }
> 
> const char *bond_slave_link_status(s8 link)
>-- 
>2.43.0
>

---
	-Jay Vosburgh, [email-masked]