From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [RFC] NETDEV_UNREGISTER_BATCH seems unused nowaday ?
Date: Fri, 10 Aug 2012 13:06:49 +0200
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To: David Miller <davem@davemloft.net>
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On Fri, 2012-08-10 at 03:42 -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Fri, 10 Aug 2012 11:27:04 +0200
> 
> > NETDEV_UNREGISTER_BATCH seems unused we can probably remove it.
> 
> Indeed, the routing cache was the final real user.
> 
> > I am tracking a device refcount issue, delaying net device dismantle by
> > 1 second in netdev_wait_allrefs()
> > 
> > I guess we need to add a notifier called _after_ the final
> > synchronize_net() in rollback_registered_many()
> 
> It's essentially caused by DST_GC_INC, right?

No, we in fact need a rcu_barrier(), then another call to
dst_dev_event().

rcu_barrier() is needed so that in-flight call_rcu() of routes (from
rt_free()) are completed. Or else we miss these dst in the
dst_dev_event().

I have a working patch, adding the rcu_barrier() and one additional
NETDEV_UNREGISTER_FINAL event.