bonding/802.3ad: fix slave link initialization transition states

Once in a while, with just the right timing, 802.3ad slaves will fail to
properly initialize, winding up in a weird state, with a partner system
mac address of 00:00:00:00:00:00. This started happening after a fix to
properly track link_failure_count tracking, where an 802.3ad slave that
reported itself as link up in the miimon code, but wasn't able to get a
valid speed/duplex, started getting set to BOND_LINK_FAIL instead of
BOND_LINK_DOWN. That was the proper thing to do for the general "my link
went down" case, but has created a link initialization race that can put
the interface in this odd state.

The simple fix is to instead set the slave link to BOND_LINK_DOWN again,
if the link has never been up (last_link_up == 0), so the link state
doesn't bounce from BOND_LINK_DOWN to BOND_LINK_FAIL -- it hasn't failed
in this case, it simply hasn't been up yet, and this prevents the
unnecessary state change from DOWN to FAIL and getting stuck in an init
failure w/o a partner mac.

Fixes: ea53abfa ("bonding/802.3ad: fix link_failure_count tracking")
CC: Jay Vosburgh <j.vosburgh@gmail.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: Andy Gospodarek <andy@greyhouse.net>
CC: "David S. Miller" <davem@davemloft.net>
CC: netdev@vger.kernel.org
Tested-by: Heesoon Kim <Heesoon.Kim@stratus.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -3122,13 +3122,18 @@ static int bond_slave_netdev_event(unsigned long event,
 	case NETDEV_CHANGE:
 		/* For 802.3ad mode only:
 		 * Getting invalid Speed/Duplex values here will put slave
-		 * in weird state. So mark it as link-fail for the time
-		 * being and let link-monitoring (miimon) set it right when
-		 * correct speeds/duplex are available.
+		 * in weird state. Mark it as link-fail if the link was
+		 * previously up or link-down if it hasn't yet come up, and
+		 * let link-monitoring (miimon) set it right when correct
+		 * speeds/duplex are available.
 		 */
 		if (bond_update_speed_duplex(slave) &&
-		    BOND_MODE(bond) == BOND_MODE_8023AD)
+		    BOND_MODE(bond) == BOND_MODE_8023AD) {
+			if (slave->last_link_up)
 				slave->link = BOND_LINK_FAIL;
+			else
+				slave->link = BOND_LINK_DOWN;
+		}
 
 		if (BOND_MODE(bond) == BOND_MODE_8023AD)
 			bond_3ad_adapter_speed_duplex_changed(slave);