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

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Message-ID: <20160415135832.773707e3@xeon-e3>
Date:	Fri, 15 Apr 2016 13:58:32 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	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>
Subject: Re: [PATCH net-next v2] vxlan: synchronously and race-free
 destruction of vxlan sockets

On Sat, 09 Apr 2016 01:55:06 +0200
Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:

> 
> 
> 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

The problem was that VXLAN needs to update multicast settings and that
can't be done under RTNL.