[PATCH net] NTB: ntb_netdev: Preserve RX queue depth on allocation failure

[Koichiro Den]

ntb_netdev_rx_handler() hands the received skb to the network stack
before allocating its replacement. If the allocation fails, nothing is
reposted. Every failure therefore takes one buffer out of the RX queue
while the interface remains up, and enough failures eventually stall
reception.

A retry path could refill the queue later, but ntb_netdev has none.
Allocate the replacement first instead. If that fails, drop the packet
and repost the same skb. This keeps the queue full and lets packet
delivery resume as soon as memory is available again.

Fixes: 548c237c0a99 ("net: Add support for NTB virtual ethernet device")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
 drivers/net/ntb_netdev.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ntb_netdev.c b/drivers/net/ntb_netdev.c
index c3a6ba96fc8a..029a4a532a10 100644
--- a/drivers/net/ntb_netdev.c
+++ b/drivers/net/ntb_netdev.c
@@ -127,8 +127,8 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data,
 {
 	struct ntb_netdev_queue *q = qp_data;
 	struct ntb_netdev *dev = q->ntdev;
+	struct sk_buff *skb, *new_skb;
 	struct net_device *ndev;
-	struct sk_buff *skb;
 	int rc;
 
 	ndev = dev->ndev;
@@ -144,6 +144,12 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data,
 		goto enqueue_again;
 	}
 
+	new_skb = netdev_alloc_skb(ndev, ndev->mtu + ETH_HLEN);
+	if (!new_skb) {
+		ndev->stats.rx_dropped++;
+		goto enqueue_again;
+	}
+
 	skb_put(skb, len);
 	skb->protocol = eth_type_trans(skb, ndev);
 	skb->ip_summed = CHECKSUM_NONE;
@@ -157,12 +163,7 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data,
 		ndev->stats.rx_bytes += len;
 	}
 
-	skb = netdev_alloc_skb(ndev, ndev->mtu + ETH_HLEN);
-	if (!skb) {
-		ndev->stats.rx_errors++;
-		ndev->stats.rx_frame_errors++;
-		return;
-	}
+	skb = new_skb;
 
 enqueue_again:
 	rc = ntb_transport_rx_enqueue(qp, skb, skb->data, ndev->mtu + ETH_HLEN);
-- 
2.51.0