net: arc_emac: fix arc_emac_rx() error paths

arc_emac_rx() has some issues found by code review.

In case netdev_alloc_skb_ip_align() or dma_map_single() failure
rx fifo entry will not be returned to EMAC.

In case dma_map_single() failure previously allocated skb became
lost to driver. At the same time address of newly allocated skb
will not be provided to EMAC.

Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/arc/emac_main.c

@@ -210,39 +210,48 @@ static int arc_emac_rx(struct net_device *ndev, int budget)
 			continue;
 		}
 
-		pktlen = info & LEN_MASK;
-		stats->rx_packets++;
-		stats->rx_bytes += pktlen;
-		skb = rx_buff->skb;
-		skb_put(skb, pktlen);
-		skb->dev = ndev;
-		skb->protocol = eth_type_trans(skb, ndev);
-
-		dma_unmap_single(&ndev->dev, dma_unmap_addr(rx_buff, addr),
-				 dma_unmap_len(rx_buff, len), DMA_FROM_DEVICE);
-
-		/* Prepare the BD for next cycle */
-		rx_buff->skb = netdev_alloc_skb_ip_align(ndev,
-							 EMAC_BUFFER_SIZE);
-		if (unlikely(!rx_buff->skb)) {
+		/* Prepare the BD for next cycle. netif_receive_skb()
+		 * only if new skb was allocated and mapped to avoid holes
+		 * in the RX fifo.
+		 */
+		skb = netdev_alloc_skb_ip_align(ndev, EMAC_BUFFER_SIZE);
+		if (unlikely(!skb)) {
+			if (net_ratelimit())
+				netdev_err(ndev, "cannot allocate skb\n");
+			/* Return ownership to EMAC */
+			rxbd->info = cpu_to_le32(FOR_EMAC | EMAC_BUFFER_SIZE);
 			stats->rx_errors++;
-			/* Because receive_skb is below, increment rx_dropped */
 			stats->rx_dropped++;
 			continue;
 		}
 
-		/* receive_skb only if new skb was allocated to avoid holes */
-		netif_receive_skb(skb);
-
-		addr = dma_map_single(&ndev->dev, (void *)rx_buff->skb->data,
+		addr = dma_map_single(&ndev->dev, (void *)skb->data,
 				      EMAC_BUFFER_SIZE, DMA_FROM_DEVICE);
 		if (dma_mapping_error(&ndev->dev, addr)) {
 			if (net_ratelimit())
-				netdev_err(ndev, "cannot dma map\n");
-			dev_kfree_skb(rx_buff->skb);
+				netdev_err(ndev, "cannot map dma buffer\n");
+			dev_kfree_skb(skb);
+			/* Return ownership to EMAC */
+			rxbd->info = cpu_to_le32(FOR_EMAC | EMAC_BUFFER_SIZE);
 			stats->rx_errors++;
+			stats->rx_dropped++;
 			continue;
 		}
+
+		/* unmap previosly mapped skb */
+		dma_unmap_single(&ndev->dev, dma_unmap_addr(rx_buff, addr),
+				 dma_unmap_len(rx_buff, len), DMA_FROM_DEVICE);
+
+		pktlen = info & LEN_MASK;
+		stats->rx_packets++;
+		stats->rx_bytes += pktlen;
+		skb_put(rx_buff->skb, pktlen);
+		rx_buff->skb->dev = ndev;
+		rx_buff->skb->protocol = eth_type_trans(rx_buff->skb, ndev);
+
+		netif_receive_skb(rx_buff->skb);
+
+		rx_buff->skb = skb;
 		dma_unmap_addr_set(rx_buff, addr, addr);
 		dma_unmap_len_set(rx_buff, len, EMAC_BUFFER_SIZE);