[TG3]: Refine napi poll loop.

Need to read and store sblk->status_tag before checking for more work.
The status tag is later written back to the hardware when enabling
interrupts to acknowledge how much work has been processed.  If the
order is reversed, we can end up acknowledging work we haven't
processed.

When we detect tx error, it is more correct to return the rx
work_done so far instead of 0.
Signed-off-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tg3.c

@@ -3576,7 +3576,7 @@ static int tg3_poll_work(struct tg3 *tp, int work_done, int budget)
 	if (sblk->idx[0].tx_consumer != tp->tx_cons) {
 		tg3_tx(tp);
 		if (unlikely(tp->tg3_flags & TG3_FLAG_TX_RECOVERY_PENDING))
-			return 0;
+			return work_done;
 	}
 
 	/* run RX thread, within the bounds set by NAPI.
@@ -3593,6 +3593,7 @@ static int tg3_poll(struct napi_struct *napi, int budget)
 {
 	struct tg3 *tp = container_of(napi, struct tg3, napi);
 	int work_done = 0;
+	struct tg3_hw_status *sblk = tp->hw_status;
 
 	while (1) {
 		work_done = tg3_poll_work(tp, work_done, budget);
@@ -3603,15 +3604,17 @@ static int tg3_poll(struct napi_struct *napi, int budget)
 		if (unlikely(work_done >= budget))
 			break;
 
-		if (likely(!tg3_has_work(tp))) {
-			struct tg3_hw_status *sblk = tp->hw_status;
-
-			if (tp->tg3_flags & TG3_FLAG_TAGGED_STATUS) {
-				tp->last_tag = sblk->status_tag;
-				rmb();
-			} else
-				sblk->status &= ~SD_STATUS_UPDATED;
+		if (tp->tg3_flags & TG3_FLAG_TAGGED_STATUS) {
+			/* tp->last_tag is used in tg3_restart_ints() below
+			 * to tell the hw how much work has been processed,
+			 * so we must read it before checking for more work.
+			 */
+			tp->last_tag = sblk->status_tag;
+			rmb();
+		} else
+			sblk->status &= ~SD_STATUS_UPDATED;
 
+		if (likely(!tg3_has_work(tp))) {
 			netif_rx_complete(tp->dev, napi);
 			tg3_restart_ints(tp);
 			break;
@@ -3621,9 +3624,10 @@ static int tg3_poll(struct napi_struct *napi, int budget)
 	return work_done;
 
 tx_recovery:
+	/* work_done is guaranteed to be less than budget. */
 	netif_rx_complete(tp->dev, napi);
 	schedule_work(&tp->reset_task);
-	return 0;
+	return work_done;
 }
 
 static void tg3_irq_quiesce(struct tg3 *tp)