[PATCH v5 net 1/4] net: enetc: reserve VLAN extension BDs for software TSO

[vladimir.oltean@nxp.com]

enetc_start_xmit() uses tso_count_descs() to check whether the TX ring
has enough free BDs for a software TSO frame. That estimates one header
BD and one data BD per segment, plus one BD per frag. However, when the
skb carries a VLAN tag, enetc_map_tx_tso_hdr() also adds an extension
BD to every segment, which is not accounted for.

With a highly segmented VLAN TSO skb and a nearly full ring, the driver
can then write past next_to_clean and overwrite BDs still owned by the
hardware.

Add enetc_tso_count_descs() which accounts for the extension BD of each
segment when VLAN insertion is needed.

Fixes: fb8629e2cbfc ("net: enetc: add support for software TSO")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
v4->v5: patch is new
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index c6571b5cc842..f6b352a3a49c 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -685,6 +685,17 @@ static int enetc_lso_count_descs(const struct sk_buff *skb)
 	return skb_shinfo(skb)->nr_frags + 4;
 }
 
+static int enetc_tso_count_descs(const struct sk_buff *skb)
+{
+	int count = tso_count_descs(skb);
+
+	/* Each segment also needs an extension BD for VLAN insertion */
+	if (skb_vlan_tag_present(skb))
+		count += skb_shinfo(skb)->gso_segs;
+
+	return count;
+}
+
 static int enetc_lso_get_hdr_len(const struct sk_buff *skb)
 {
 	int hdr_len, tlen;
@@ -1029,7 +1040,7 @@ static netdev_tx_t enetc_start_xmit(struct sk_buff *skb,
 
 			count = enetc_lso_hw_offload(tx_ring, skb);
 		} else {
-			if (enetc_bd_unused(tx_ring) < tso_count_descs(skb)) {
+			if (enetc_bd_unused(tx_ring) < enetc_tso_count_descs(skb)) {
 				netif_stop_subqueue(ndev, tx_ring->index);
 				return NETDEV_TX_BUSY;
 			}
-- 
2.43.0