netdev - Re: [PATCH net-next v2] vxlan: synchronously and race-free destruction of vxlan sockets

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Date:	Sat, 09 Apr 2016 01:55:06 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Jiri Benc <jbenc@...hat.com>,
	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net-next v2] vxlan: synchronously and race-free destruction
 of vxlan sockets



On Sat, Apr 9, 2016, at 01:24, Cong Wang wrote:
> On Fri, Apr 8, 2016 at 1:55 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> > Due to the fact that the udp socket is destructed asynchronously in a
> > work queue, we have some nondeterministic behavior during shutdown of
> > vxlan tunnels and creating new ones. Fix this by keeping the destruction
> > process synchronous in regards to the user space process so IFF_UP can
> > be reliably set.
> >
> > udp_tunnel_sock_release destroys vs->sock->sk if reference counter
> > indicates so. We expect to have the same lifetime of vxlan_sock and
> > vxlan_sock->sock->sk even in fast paths with only rcu locks held. So
> > only destruct the whole socket after we can be sure it cannot be found
> > by searching vxlan_net->sock_list.
> >
> 
> I am wondering what is the reason why we used work queue from
> the beginning?

I actually don't know. It was like that from the beginning. I cc'ed
Stephen, maybe he remembers?

Bye,
Hannes