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

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Date:	Thu, 23 Aug 2012 19:21:18 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, <gaofeng@...fujitsu.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

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

So what happens when this races with register_netdevice_notifier()?

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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