drivers/net: fixed drivers that support netpoll use ndo_start_xmit()

The NETPOLL API requires that interrupts remain disabled in
netpoll_send_skb(). The use of "A functions set" in the NETPOLL API
callbacks causes the interrupts to get enabled and can lead to kernel
instability.

The solution is to use "B functions set" to prevent the irqs from
getting enabled while in netpoll_send_skb().

A functions set:
local_irq_disable()/local_irq_enable()
spin_lock_irq()/spin_unlock_irq()
spin_trylock_irq()/spin_unlock_irq()

B functions set:
local_irq_save()/local_irq_restore()
spin_lock_irqsave()/spin_unlock_irqrestore()
spin_trylock_irqsave()/spin_unlock_irqrestore()

Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macb.c

@@ -620,6 +620,7 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	dma_addr_t mapping;
 	unsigned int len, entry;
 	u32 ctrl;
+	unsigned long flags;
 
 #ifdef DEBUG
 	int i;
@@ -635,12 +636,12 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 #endif
 
 	len = skb->len;
-	spin_lock_irq(&bp->lock);
+	spin_lock_irqsave(&bp->lock, flags);
 
 	/* This is a hard error, log it. */
 	if (TX_BUFFS_AVAIL(bp) < 1) {
 		netif_stop_queue(dev);
-		spin_unlock_irq(&bp->lock);
+		spin_unlock_irqrestore(&bp->lock, flags);
 		dev_err(&bp->pdev->dev,
 			"BUG! Tx Ring full when queue awake!\n");
 		dev_dbg(&bp->pdev->dev, "tx_head = %u, tx_tail = %u\n",
@@ -674,7 +675,7 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (TX_BUFFS_AVAIL(bp) < 1)
 		netif_stop_queue(dev);
 
-	spin_unlock_irq(&bp->lock);
+	spin_unlock_irqrestore(&bp->lock, flags);
 
 	dev->trans_start = jiffies;