net: devinet: Reduce refcount before grace period

Currently, the inetdev_destroy() function waits for an RCU grace period
before decrementing the refcount and freeing memory. This causes a delay
with a new RCU configuration that tries to save power, which results in the
network interface disappearing later than expected. The resulting delay
causes test failures on ChromeOS.

Refactor the code such that the refcount is freed before the grace period
and memory is freed after. With this a ChromeOS network test passes that
does 'ip netns del' and polls for an interface disappearing, now passes.

Reported-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: Joel Fernandes (Google) <[email protected]>
Cc: David Ahern <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Hideaki YOSHIFUJI <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>

Author: edumazet

net/ipv4/devinet.c

@@ -234,21 +234,28 @@ static void inet_free_ifa(struct in_ifaddr *ifa)
 	call_rcu(&ifa->rcu_head, inet_rcu_free_ifa);
 }
 
+static void in_dev_free_rcu(struct rcu_head *head)
+{
+	struct in_device *idev = container_of(head, struct in_device, rcu_head);
+
+	kfree(rcu_dereference_protected(idev->mc_hash, 1));
+	kfree(idev);
+}
+
 void in_dev_finish_destroy(struct in_device *idev)
 {
 	struct net_device *dev = idev->dev;
 
 	WARN_ON(idev->ifa_list);
 	WARN_ON(idev->mc_list);
-	kfree(rcu_dereference_protected(idev->mc_hash, 1));
 #ifdef NET_REFCNT_DEBUG
 	pr_debug("%s: %p=%s\n", __func__, idev, dev ? dev->name : "NIL");
 #endif
 	netdev_put(dev, &idev->dev_tracker);
 	if (!idev->dead)
 		pr_err("Freeing alive in_device %p\n", idev);
 	else
-		kfree(idev);
+		call_rcu(&idev->rcu_head, in_dev_free_rcu);
 }
 EXPORT_SYMBOL(in_dev_finish_destroy);
 
@@ -298,12 +305,6 @@ static struct in_device *inetdev_init(struct net_device *dev)
 	goto out;
 }
 
-static void in_dev_rcu_put(struct rcu_head *head)
-{
-	struct in_device *idev = container_of(head, struct in_device, rcu_head);
-	in_dev_put(idev);
-}
-
 static void inetdev_destroy(struct in_device *in_dev)
 {
 	struct net_device *dev;
@@ -328,7 +329,7 @@ static void inetdev_destroy(struct in_device *in_dev)
 	neigh_parms_release(&arp_tbl, in_dev->arp_parms);
 	arp_ifdown(dev);
 
-	call_rcu(&in_dev->rcu_head, in_dev_rcu_put);
+	in_dev_put(in_dev);
 }
 
 int inet_addr_onlink(struct in_device *in_dev, __be32 a, __be32 b)