net: bcmgenet: check harder for out of memory conditions

There is a potential case where we might be failing to refill a
control block, leaving it with both a NULL skb pointer *and* a NULL
dma_unmap_addr.

The way we process incoming packets, by first calling
dma_unmap_single(), and then only checking for a potential NULL skb can
lead to situations where do pass a NULL dma_unmap_addr() to
dma_unmap_single(), resulting in an oops.

Fix this my moving the NULL skb check earlier, since no backing skb
also means no corresponding DMA mapping for this packet.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 19 insertions, 14 deletions

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index 3f9d4de8173c..cdef86a03862 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -1274,12 +1274,29 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_priv *priv,
 
         while ((rxpktprocessed < rxpkttoprocess) &&
                (rxpktprocessed < budget)) {
+                cb = &priv->rx_cbs[priv->rx_read_ptr];
+                skb = cb->skb;
+
+                rxpktprocessed++;
+
+                priv->rx_read_ptr++;
+                priv->rx_read_ptr &= (priv->num_rx_bds - 1);
+
+                /* We do not have a backing SKB, so we do not have a
+                 * corresponding DMA mapping for this incoming packet since
+                 * bcmgenet_rx_refill always either has both skb and mapping or
+                 * none.
+                 */
+                if (unlikely(!skb)) {
+                        dev->stats.rx_dropped++;
+                        dev->stats.rx_errors++;
+                        goto refill;
+                }
+
                 /* Unmap the packet contents such that we can use the
                  * RSV from the 64 bytes descriptor when enabled and save
                  * a 32-bits register read
                  */
-                cb = &priv->rx_cbs[priv->rx_read_ptr];
-                skb = cb->skb;
                 dma_unmap_single(&dev->dev, dma_unmap_addr(cb, dma_addr),
                                  priv->rx_buf_len, DMA_FROM_DEVICE);
 
@@ -1307,18 +1324,6 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_priv *priv,
                           __func__, p_index, priv->rx_c_index,
                           priv->rx_read_ptr, dma_length_status);
 
-                rxpktprocessed++;
-
-                priv->rx_read_ptr++;
-                priv->rx_read_ptr &= (priv->num_rx_bds - 1);
-
-                /* out of memory, just drop packets at the hardware level */
-                if (unlikely(!skb)) {
-                        dev->stats.rx_dropped++;
-                        dev->stats.rx_errors++;
-                        goto refill;
-                }
-
                 if (unlikely(!(dma_flag & DMA_EOP) || !(dma_flag & DMA_SOP))) {
                         netif_err(priv, rx_status, dev,
                                   "dropping fragmented packet!\n");