From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gao feng <gaofeng@cn.fujitsu.com>
Subject: Re: [PATCH net-next v3] net: remove delay at device dismantle
Date: Thu, 23 Aug 2012 12:33:03 +0800
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Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org,
	maheshb@google.com, therbert@google.com, ebiederm@xmission.com
To: Eric Dumazet <eric.dumazet@gmail.com>
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=E4=BA=8E 2012=E5=B9=B408=E6=9C=8823=E6=97=A5 11:19, Eric Dumazet =E5=86=
=99=E9=81=93:
> From: Eric Dumazet <edumazet@google.com>
>=20
> 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 queu=
es.
>=20
> These call_rcu() were posted by rt_free(struct rtable *rt) calls.
>=20
> We then wait a little (but one second) in netdev_wait_allrefs() befor=
e
> kicking again NETDEV_UNREGISTER.
>=20
> As the call_rcu() are now completed, dst_dev_event() can do the neede=
d
> device swap on busy dst.
>=20
> To solve this problem, add a new NETDEV_UNREGISTER_FINAL, called
> after a rcu_barrier(), but outside of RTNL lock.
>=20
> Use NETDEV_UNREGISTER_FINAL with care !
>=20
> Change dst_dev_event() handler to react to NETDEV_UNREGISTER_FINAL
>=20
> Also remove NETDEV_UNREGISTER_BATCH, as its not used anymore after
> IP cache removal.
>=20
> With help from Gao feng
>=20
> 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>

looks good to me, the lockdep warning message disappeared.