[PATCH net-next 2/2] ipvlan: avoid spinlock contention in ipvlan_multicast_enqueue()

[Eric Dumazet <edumazet@google.com>]

Under high stress, we spend a lot of time cloning skbs,
then acquiring a spinlock, then freeing the clone because
the queue is full.

Add a shortcut to avoid these costs under pressure, as we did
in macvlan with commit 0d5dc1d7aad1 ("macvlan: avoid spinlock
contention in macvlan_broadcast_enqueue()")

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/ipvlan/ipvlan_core.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ipvlan/ipvlan_core.c b/drivers/net/ipvlan/ipvlan_core.c
index 214fd299a5aa6e40579aa2dbcb178b5474b561a4..1be8620ad3971d281fb36fd0770efd67b566ae60 100644
--- a/drivers/net/ipvlan/ipvlan_core.c
+++ b/drivers/net/ipvlan/ipvlan_core.c
@@ -763,10 +763,16 @@ static rx_handler_result_t ipvlan_handle_mode_l2(struct sk_buff **pskb,
 	if (!ipvlan_external_frame(skb, port))
 		return RX_HANDLER_PASS;
 
-	nskb = skb_clone(skb, GFP_ATOMIC);
+	if (skb_queue_len_lockless(&port->backlog) >= IPVLAN_QBACKLOG_LIMIT)
+		nskb = NULL;
+	else
+		nskb = skb_clone(skb, GFP_ATOMIC);
+
 	if (nskb) {
 		ipvlan_skb_crossing_ns(nskb, NULL);
 		ipvlan_multicast_enqueue(port, nskb, false);
+	} else {
+		dev_core_stats_rx_dropped_inc(skb->dev);
 	}
 
 	return RX_HANDLER_PASS;
-- 
2.53.0.1213.gd9a14994de-goog