[PATCH 7.1 217/271] NTB: ntb_netdev: Preserve RX queue depth on allocation failure

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

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

From: Koichiro Den <[email protected]>

commit d2121faf133ac3bf9531b53a7e21273649a08517 upstream.

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: [email protected]
Signed-off-by: Koichiro Den <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/ntb_netdev.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

--- a/drivers/net/ntb_netdev.c
+++ b/drivers/net/ntb_netdev.c
@@ -127,8 +127,8 @@ static void ntb_netdev_rx_handler(struct
 {
 	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
 		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
 		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);