netdev - Re: [PATCH net] vxlan: synchronously and race-free destruction of vxlan sockets

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Message-ID: <1460148028.6473.446.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Fri, 08 Apr 2016 13:40:28 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
	netdev@...r.kernel.org, Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH net] vxlan: synchronously and race-free destruction of
 vxlan sockets

On Fri, 2016-04-08 at 22:30 +0200, Hannes Frederic Sowa wrote:
> Hi Marcelo,
> ng rtnl?
> 
> I thought about that and try not to use synchronize_rcu, but I don't see 
> any other way. Anyway, ndo_stop isn't really fast path and is used to 
> shut the interface down. Also since we have lwtunnels we don't really 
> need a lot of interfaces created and torn down.
> 
> But I could switch to synchronize_rcu_expedited here.
> 
> Also we have another synchronize_rcu during device dismantling, maybe we 
> can split ndo_stop into two callbacks, one preparing for stopping and 
> the other one after the synchronize_rcu when we safely can free resources.
> 
> I will investigate this but for the mean time I think this patch is 
> already improving things as user space can bind the socket again when 
> the dellink command returned.

Of course, we have synchronize_net() which specifically put in a single
point the knowledge (rtnl being held or not)