[PATCH v6 2/4] net: moxa: replace build_skb() with netdev_alloc_skb_ip_align() / memcpy()

[Jonas Jensen]

build_skb() is used to make skbs out of existing RX ring memory
which is bad because the RX ring is allocated only once, on probe.
Memory corruption occur because said memory is reclaimed, i.e.
__kfree_skb() (and eventually put_page()).

Replace build_skb() with netdev_alloc_skb_ip_align() and use memcpy().

Remove SKB_DATA_ALIGN() from RX buffer size while we're at it.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=69041

Signed-off-by: Jonas Jensen <jonas.jensen at gmail.com>
---

Notes:
    Changes since v5:
    
    1. broke out DMA synchronization to separate patch
    
    Applies to next-20140825

 drivers/net/ethernet/moxa/moxart_ether.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/moxa/moxart_ether.c b/drivers/net/ethernet/moxa/moxart_ether.c
index eed70d9..d66058d 100644
--- a/drivers/net/ethernet/moxa/moxart_ether.c
+++ b/drivers/net/ethernet/moxa/moxart_ether.c
@@ -226,13 +226,15 @@ static int moxart_rx_poll(struct napi_struct *napi, int budget)
 		if (len > RX_BUF_SIZE)
 			len = RX_BUF_SIZE;
 
-		skb = build_skb(priv->rx_buf[rx_head], priv->rx_buf_size);
+		skb = netdev_alloc_skb_ip_align(ndev, len);
+
 		if (unlikely(!skb)) {
-			net_dbg_ratelimited("build_skb failed\n");
+			net_dbg_ratelimited("netdev_alloc_skb_ip_align failed\n");
 			priv->stats.rx_dropped++;
 			priv->stats.rx_errors++;
 		}
 
+		memcpy(skb->data, priv->rx_buf[rx_head], len);
 		skb_put(skb, len);
 		skb->protocol = eth_type_trans(skb, ndev);
 		napi_gro_receive(&priv->napi, skb);
@@ -464,8 +466,7 @@ static int moxart_mac_probe(struct platform_device *pdev)
 	spin_lock_init(&priv->txlock);
 
 	priv->tx_buf_size = TX_BUF_SIZE;
-	priv->rx_buf_size = RX_BUF_SIZE +
-			    SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	priv->rx_buf_size = RX_BUF_SIZE;
 
 	priv->tx_desc_base = dma_alloc_coherent(NULL, TX_REG_DESC_SIZE *
 						TX_DESC_NUM, &priv->tx_base,
-- 
1.8.2.1