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, 4 insertions, 4 deletions

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 7f073a38c87d..fd7d9ae64f16 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1041,7 +1041,7 @@ static int fib_inetaddr_event(struct notifier_block *this, unsigned long event,
 static int fib_netdev_event(struct notifier_block *this, unsigned long event, void *ptr)
 {
         struct net_device *dev = ptr;
-        struct in_device *in_dev = __in_dev_get_rtnl(dev);
+        struct in_device *in_dev;
         struct net *net = dev_net(dev);
 
         if (event == NETDEV_UNREGISTER) {
@@ -1050,9 +1050,11 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
                 return NOTIFY_DONE;
         }
 
-        if (!in_dev)
+        if (event == NETDEV_UNREGISTER_FINAL)
                 return NOTIFY_DONE;
 
+        in_dev = __in_dev_get_rtnl(dev);
+
         switch (event) {
         case NETDEV_UP:
                 for_ifa(in_dev) {
@@ -1071,8 +1073,6 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
         case NETDEV_CHANGE:
                 rt_cache_flush(dev_net(dev), 0);
                 break;
-        case NETDEV_UNREGISTER_BATCH:
-                break;
         }
         return NOTIFY_DONE;
 }