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

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Date:	Thu, 23 Aug 2012 12:33:03 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	maheshb@...gle.com, therbert@...gle.com, ebiederm@...ssion.com
Subject: Re: [PATCH net-next v3] net: remove delay at device dismantle

于 2012年08月23日 11:19, Eric Dumazet 写道:
> From: Eric Dumazet <edumazet@...gle.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.
> 
> 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@...gle.com>
> Cc: Tom Herbert <therbert@...gle.com>
> Cc: Mahesh Bandewar <maheshb@...gle.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Gao feng <gaofeng@...fujitsu.com>

looks good to me, the lockdep warning message disappeared.

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