skge: fix occasional BUG during MTU change

The BUG_ON(skge->tx_ring.to_use != skge->tx_ring.to_clean) in skge_up()
was sometimes observed when setting MTU.

skge_down() disables the TX queue, but then reenables it by mistake via
skge_tx_clean().
Fix it by moving the waking of the queue from skge_tx_clean() to the
other caller. And to make sure start_xmit is not in progress on another
CPU, skge_down() should call netif_tx_disable().

The bug was reported to me by Jiri Jilek whose Debian system sometimes
failed to boot. He tested the patch and the bug did not happen anymore.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/skge.c

@@ -2674,7 +2674,7 @@ static int skge_down(struct net_device *dev)
 	if (netif_msg_ifdown(skge))
 		printk(KERN_INFO PFX "%s: disabling interface\n", dev->name);
 
-	netif_stop_queue(dev);
+	netif_tx_disable(dev);
 
 	if (hw->chip_id == CHIP_ID_GENESIS && hw->phy_type == SK_PHY_XMAC)
 		del_timer_sync(&skge->link_timer);
@@ -2881,7 +2881,6 @@ static void skge_tx_clean(struct net_device *dev)
 	}
 
 	skge->tx_ring.to_clean = e;
-	netif_wake_queue(dev);
 }
 
 static void skge_tx_timeout(struct net_device *dev)
@@ -2893,6 +2892,7 @@ static void skge_tx_timeout(struct net_device *dev)
 
 	skge_write8(skge->hw, Q_ADDR(txqaddr[skge->port], Q_CSR), CSR_STOP);
 	skge_tx_clean(dev);
+	netif_wake_queue(dev);
 }
 
 static int skge_change_mtu(struct net_device *dev, int new_mtu)