Revert "r8169: make use of xmit_more and __netdev_sent_queue"

This reverts commit 2e6eedb4.

Sander reported a regression causing a kernel panic[1],
therefore let's revert this commit.

[1] https://marc.info/?t=154965066400001&r=1&w=2Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169.c

@@ -6074,7 +6074,6 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 	struct device *d = tp_to_dev(tp);
 	dma_addr_t mapping;
 	u32 opts[2], len;
-	bool stop_queue;
 	int frags;
 
 	if (unlikely(!rtl_tx_slots_avail(tp, skb_shinfo(skb)->nr_frags))) {
@@ -6116,6 +6115,8 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	txd->opts2 = cpu_to_le32(opts[1]);
 
+	netdev_sent_queue(dev, skb->len);
+
 	skb_tx_timestamp(skb);
 
 	/* Force memory writes to complete before releasing descriptor */
@@ -6128,16 +6129,16 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	tp->cur_tx += frags + 1;
 
-	stop_queue = !rtl_tx_slots_avail(tp, MAX_SKB_FRAGS);
-	if (unlikely(stop_queue))
-		netif_stop_queue(dev);
+	RTL_W8(tp, TxPoll, NPQ);
 
-	if (__netdev_sent_queue(dev, skb->len, skb->xmit_more)) {
-		RTL_W8(tp, TxPoll, NPQ);
-		mmiowb();
-	}
+	mmiowb();
 
-	if (unlikely(stop_queue)) {
+	if (!rtl_tx_slots_avail(tp, MAX_SKB_FRAGS)) {
+		/* Avoid wrongly optimistic queue wake-up: rtl_tx thread must
+		 * not miss a ring update when it notices a stopped queue.
+		 */
+		smp_wmb();
+		netif_stop_queue(dev);
 		/* Sync with rtl_tx:
 		 * - publish queue status and cur_tx ring index (write barrier)
 		 * - refresh dirty_tx ring index (read barrier).