ipv6: add (struct uncached_list)->quarantine list

This is an optimization to keep the per-cpu lists as short as possible:

Whenever rt6_uncached_list_flush_dev() changes one rt6_info
matching the disappearing device, it can can transfer the object
to a quarantine list, waiting for a final rt6_uncached_list_del().
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -130,6 +130,7 @@ static struct fib6_info *rt6_get_route_info(struct net *net,
 struct uncached_list {
 	spinlock_t		lock;
 	struct list_head	head;
+	struct list_head	quarantine;
 };
 
 static DEFINE_PER_CPU_ALIGNED(struct uncached_list, rt6_uncached_list);
@@ -151,7 +152,7 @@ void rt6_uncached_list_del(struct rt6_info *rt)
 		struct uncached_list *ul = rt->rt6i_uncached_list;
 
 		spin_lock_bh(&ul->lock);
-		list_del(&rt->rt6i_uncached);
+		list_del_init(&rt->rt6i_uncached);
 		spin_unlock_bh(&ul->lock);
 	}
 }
@@ -162,16 +163,21 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev)
 
 	for_each_possible_cpu(cpu) {
 		struct uncached_list *ul = per_cpu_ptr(&rt6_uncached_list, cpu);
-		struct rt6_info *rt;
+		struct rt6_info *rt, *safe;
+
+		if (list_empty(&ul->head))
+			continue;
 
 		spin_lock_bh(&ul->lock);
-		list_for_each_entry(rt, &ul->head, rt6i_uncached) {
+		list_for_each_entry_safe(rt, safe, &ul->head, rt6i_uncached) {
 			struct inet6_dev *rt_idev = rt->rt6i_idev;
 			struct net_device *rt_dev = rt->dst.dev;
+			bool handled = false;
 
 			if (rt_idev->dev == dev) {
 				rt->rt6i_idev = in6_dev_get(blackhole_netdev);
 				in6_dev_put(rt_idev);
+				handled = true;
 			}
 
 			if (rt_dev == dev) {
@@ -179,7 +185,11 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev)
 				dev_replace_track(rt_dev, blackhole_netdev,
 						  &rt->dst.dev_tracker,
 						  GFP_ATOMIC);
+				handled = true;
 			}
+			if (handled)
+				list_move(&rt->rt6i_uncached,
+					  &ul->quarantine);
 		}
 		spin_unlock_bh(&ul->lock);
 	}
@@ -6727,6 +6737,7 @@ int __init ip6_route_init(void)
 		struct uncached_list *ul = per_cpu_ptr(&rt6_uncached_list, cpu);
 
 		INIT_LIST_HEAD(&ul->head);
+		INIT_LIST_HEAD(&ul->quarantine);
 		spin_lock_init(&ul->lock);
 	}