[PATCH 3.16 009/294] net: bcmgenet: check harder for out of memory conditions

[Ben Hutchings]

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Fainelli <f.fainelli@xxxxxxxxx>

commit b629be5c8399d7c423b92135eb43a86c924d1cbc upstream.

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@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 33 +++++++++++++++-----------
 1 file changed, 19 insertions(+), 14 deletions(-)

--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -1351,12 +1351,29 @@ static unsigned int bcmgenet_desc_rx(str
 	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(kdev, dma_unmap_addr(cb, dma_addr),
 				priv->rx_buf_len, DMA_FROM_DEVICE);
 
@@ -1382,18 +1399,6 @@ static unsigned int bcmgenet_desc_rx(str
 			__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,
 					"Droping fragmented packet!\n");