Re: [PATCH net-next v3] net: remove delay at device dismantle

On Thu, 2012-08-23 at 05:19 +0200, Eric Dumazet wrote:

From: Eric Dumazet <edumazet@google.com>

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.

[...]

So what happens when this races with register_netdevice_notifier()?

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
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