[PATCH net v2 2/2] net: bcmgenet: flatten frames that cannot fit the ring

[Nicolai Buchwitz]

bcmgenet_xmit() wants one descriptor more than the frame needs. A 31
fragment frame needs 32 descriptors, so it is refused on a 32 descriptor
ring, even if the ring is empty.

As a result nothing is in flight which could wake the queue again. The
watchdog can only hand the same frame back, therefore the queue stays
stopped.

This needs CONFIG_MAX_SKB_FRAGS >= 31 and a sender which fragments that
finely, for example MSG_ZEROCOPY.

Linearize those frames instead.

Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAGS")
Signed-off-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index 9049822012d13..61f5a4c2f0cd9 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -2143,6 +2143,22 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	nr_frags = skb_shinfo(skb)->nr_frags;
 
+	/* The check below would always refuse this frame */
+	if (unlikely(nr_frags + 1 >= ring->size)) {
+		skb = skb_share_check(skb, GFP_ATOMIC);
+		if (skb && skb_linearize(skb)) {
+			dev_kfree_skb_any(skb);
+			skb = NULL;
+		}
+		if (!skb) {
+			spin_lock(&ring->lock);
+			BCMGENET_STATS64_INC((&ring->stats64), dropped);
+			ret = NETDEV_TX_OK;
+			goto out;
+		}
+		nr_frags = 0;
+	}
+
 	spin_lock(&ring->lock);
 	if (ring->free_bds <= (nr_frags + 1)) {
 		if (!netif_tx_queue_stopped(txq))

-- 
2.53.0