net: hns3: fix for TX queue not restarted problem

There is timing window between ring_space checking and
netif_stop_subqueue when transmiting a SKB, and the TX BD
cleaning may be executed during the time window, which may
caused TX queue not restarted problem.

This patch fixes it by rechecking the ring_space after
netif_stop_subqueue to make sure TX queue is restarted.

Also, the ring->next_to_clean is updated even when pkts is
zero, because all the TX BD cleaned may be non-SKB, so it
needs to check if TX queue need to be restarted.

Fixes: 76ad4f0e ("net: hns3: Add support of HNS3 Ethernet Driver for hip08 SoC")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hns3/hns3_enet.c

@@ -1287,8 +1287,10 @@ static bool hns3_skb_need_linearized(struct sk_buff *skb, unsigned int *bd_size,
 }
 
 static int hns3_nic_maybe_stop_tx(struct hns3_enet_ring *ring,
+				  struct net_device *netdev,
 				  struct sk_buff **out_skb)
 {
+	struct hns3_nic_priv *priv = netdev_priv(netdev);
 	unsigned int bd_size[HNS3_MAX_TSO_BD_NUM + 1U];
 	struct sk_buff *skb = *out_skb;
 	unsigned int bd_num;
@@ -1320,10 +1322,23 @@ static int hns3_nic_maybe_stop_tx(struct hns3_enet_ring *ring,
 	}
 
 out:
-	if (unlikely(ring_space(ring) < bd_num))
-		return -EBUSY;
+	if (likely(ring_space(ring) >= bd_num))
+		return bd_num;
 
-	return bd_num;
+	netif_stop_subqueue(netdev, ring->queue_index);
+	smp_mb(); /* Memory barrier before checking ring_space */
+
+	/* Start queue in case hns3_clean_tx_ring has just made room
+	 * available and has not seen the queue stopped state performed
+	 * by netif_stop_subqueue above.
+	 */
+	if (ring_space(ring) >= bd_num && netif_carrier_ok(netdev) &&
+	    !test_bit(HNS3_NIC_STATE_DOWN, &priv->state)) {
+		netif_start_subqueue(netdev, ring->queue_index);
+		return bd_num;
+	}
+
+	return -EBUSY;
 }
 
 static void hns3_clear_desc(struct hns3_enet_ring *ring, int next_to_use_orig)
@@ -1400,13 +1415,13 @@ netdev_tx_t hns3_nic_net_xmit(struct sk_buff *skb, struct net_device *netdev)
 	/* Prefetch the data used later */
 	prefetch(skb->data);
 
-	ret = hns3_nic_maybe_stop_tx(ring, &skb);
+	ret = hns3_nic_maybe_stop_tx(ring, netdev, &skb);
 	if (unlikely(ret <= 0)) {
 		if (ret == -EBUSY) {
 			u64_stats_update_begin(&ring->syncp);
 			ring->stats.tx_busy++;
 			u64_stats_update_end(&ring->syncp);
-			goto out_net_tx_busy;
+			return NETDEV_TX_BUSY;
 		} else if (ret == -ENOMEM) {
 			u64_stats_update_begin(&ring->syncp);
 			ring->stats.sw_err_cnt++;
@@ -1457,12 +1472,6 @@ netdev_tx_t hns3_nic_net_xmit(struct sk_buff *skb, struct net_device *netdev)
 out_err_tx_ok:
 	dev_kfree_skb_any(skb);
 	return NETDEV_TX_OK;
-
-out_net_tx_busy:
-	netif_stop_subqueue(netdev, ring->queue_index);
-	smp_mb(); /* Commit all data before submit */
-
-	return NETDEV_TX_BUSY;
 }
 
 static int hns3_nic_net_set_mac_address(struct net_device *netdev, void *p)
@@ -2519,7 +2528,7 @@ void hns3_clean_tx_ring(struct hns3_enet_ring *ring)
 	dev_queue = netdev_get_tx_queue(netdev, ring->tqp->tqp_index);
 	netdev_tx_completed_queue(dev_queue, pkts, bytes);
 
-	if (unlikely(pkts && netif_carrier_ok(netdev) &&
+	if (unlikely(netif_carrier_ok(netdev) &&
 		     ring_space(ring) > HNS3_MAX_TSO_BD_NUM)) {
 		/* Make sure that anybody stopping the queue after this
 		 * sees the new next_to_clean.