[TG3]: Fix missing memory barriers and SD_STATUS_UPDATED bit clearing.

There must be a rmb() between reading the status block tag
and calling tg3_has_work().  This was missing in tg3_mis()
and tg3_interrupt_tagged().  tg3_poll() got it right.

Also, SD_STATUS_UPDATED must be cleared in the status block
right before we call tg3_has_work().  Only tg3_poll() got this
wrong.

Based upon patches and commentary from Grant Grundler and
Michael Chan.
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tg3.c

@@ -2929,6 +2929,7 @@ static int tg3_poll(struct net_device *netdev, int *budget)
 	if (tp->tg3_flags & TG3_FLAG_TAGGED_STATUS)
 		tp->last_tag = sblk->status_tag;
 	rmb();
+	sblk->status &= ~SD_STATUS_UPDATED;
 
 	/* if no more work, tell net stack and NIC we're done */
 	done = !tg3_has_work(tp);
@@ -2964,6 +2965,7 @@ static irqreturn_t tg3_msi(int irq, void *dev_id, struct pt_regs *regs)
 	 */
 	tw32_mailbox(MAILBOX_INTERRUPT_0 + TG3_64BIT_REG_LOW, 0x00000001);
 	tp->last_tag = sblk->status_tag;
+	rmb();
 	sblk->status &= ~SD_STATUS_UPDATED;
 	if (likely(tg3_has_work(tp)))
 		netif_rx_schedule(dev);		/* schedule NAPI poll */
@@ -3051,6 +3053,7 @@ static irqreturn_t tg3_interrupt_tagged(int irq, void *dev_id, struct pt_regs *r
 		tw32_mailbox(MAILBOX_INTERRUPT_0 + TG3_64BIT_REG_LOW,
 			     0x00000001);
 		tp->last_tag = sblk->status_tag;
+		rmb();
 		sblk->status &= ~SD_STATUS_UPDATED;
 		if (likely(tg3_has_work(tp)))
 			netif_rx_schedule(dev);		/* schedule NAPI poll */