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

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Message-Id: <20120822.215054.1560262447672200871.davem@davemloft.net>
Date:	Wed, 22 Aug 2012 21:50:54 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	gaofeng@...fujitsu.com
Cc:	eric.dumazet@...il.com, 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

From: Gao feng <gaofeng@...fujitsu.com>
Date: Thu, 23 Aug 2012 12:33:03 +0800

> 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.

Applied, thanks everyone.
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