bonding: only set speed/duplex to unknown, if getting speed failed

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 691b2bf ("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: 98f41f6 ("bonding:update speed/duplex for NETDEV_CHANGE")
Signed-off-by: Thomas Bogendoerfer <[email protected]>
Acked-by: Jay Vosburgh <[email protected]>
Reviewed-by: Nikolay Aleksandrov <[email protected]>
Reviewed-by: Hangbin Liu <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Thomas Bogendoerfer

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)