net: remove delay at device dismantle

I noticed extra one second delay in device dismantle, tracked down to
a call to dst_dev_event() while some call_rcu() are still in RCU queues.

These call_rcu() were posted by rt_free(struct rtable *rt) calls.

We then wait a little (but one second) in netdev_wait_allrefs() before
kicking again NETDEV_UNREGISTER.

As the call_rcu() are now completed, dst_dev_event() can do the needed
device swap on busy dst.

To solve this problem, add a new NETDEV_UNREGISTER_FINAL, called
after a rcu_barrier(), but outside of RTNL lock.

Use NETDEV_UNREGISTER_FINAL with care !

Change dst_dev_event() handler to react to NETDEV_UNREGISTER_FINAL

Also remove NETDEV_UNREGISTER_BATCH, as its not used anymore after
IP cache removal.

With help from Gao feng

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index ab7db83236c9..585093755c23 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -711,15 +711,16 @@ static int fib_rules_event(struct notifier_block *this, unsigned long event,
 	struct net *net = dev_net(dev);
 	struct fib_rules_ops *ops;
 
-	ASSERT_RTNL();
 
 	switch (event) {
 	case NETDEV_REGISTER:
+		ASSERT_RTNL();
 		list_for_each_entry(ops, &net->rules_ops, list)
 			attach_rules(&ops->rules_list, dev);
 		break;
 
 	case NETDEV_UNREGISTER:
+		ASSERT_RTNL();
 		list_for_each_entry(ops, &net->rules_ops, list)
 			detach_rules(&ops->rules_list, dev);
 		break;