[PATCH 4.9 12/84] nfp: fix infinite loop on umapping cleanup

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>


[ Upstream commit eac2c68d663effb077210218788952b5a0c1f60e ]

The while loop that performs the dma page unmapping never decrements
index counter f and hence loops forever. Fix this with a pre-decrement
on f.

Detected by CoverityScan, CID#1357309 ("Infinite loop")

Fixes: 4c3523623dc0 ("net: add driver for Netronome NFP4000/NFP6000 NIC VFs")
Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Acked-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/netronome/nfp/nfp_net_common.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
@@ -871,8 +871,7 @@ static int nfp_net_tx(struct sk_buff *sk
 	return NETDEV_TX_OK;
 
 err_unmap:
-	--f;
-	while (f >= 0) {
+	while (--f >= 0) {
 		frag = &skb_shinfo(skb)->frags[f];
 		dma_unmap_page(&nn->pdev->dev,
 			       tx_ring->txbufs[wr_idx].dma_addr,