[PATCH 3/3] tg3: Fix tx_pending check for MAX_SKB_FRAGS

[Benjamin Poirier <bpoirier@suse.de>]

The rest of the driver assumes at least one free descriptor in the tx ring.
Therefore, since an skb with max frags takes up (MAX_SKB_FRAGS + 1)
descriptors, tx_pending must be > (MAX_SKB_FRAGS + 1).

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
---

Currently, it is possible to set tx_pending = MAX_SKB_FRAGS + 1. This leads to
a netdev watchdog tx timeout. Depending on whether the previous patches in
this series are applied or not, the timeout happens as soon as tx_pending is
updated or after an skb with max frags is submitted for transmission.

I reproduced this bug using the same approach explained in patch 1.
The bug reproduces with tx_pending = 18

---
 drivers/net/ethernet/broadcom/tg3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index 7022f6d..27e2701 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -12328,7 +12328,7 @@ static int tg3_set_ringparam(struct net_device *dev, struct ethtool_ringparam *e
 	if ((ering->rx_pending > tp->rx_std_ring_mask) ||
 	    (ering->rx_jumbo_pending > tp->rx_jmb_ring_mask) ||
 	    (ering->tx_pending > TG3_TX_RING_SIZE - 1) ||
-	    (ering->tx_pending <= MAX_SKB_FRAGS))
+	    (ering->tx_pending <= MAX_SKB_FRAGS + 1))
 		return -EINVAL;
 
 	if (netif_running(dev)) {
-- 
1.8.4.5