netdev - Re: [PATCH net-next 03/10] vxlan: move IGMP join/leave to work queue

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Message-ID: <20130605084116.4eb9dc94@nehalam.linuxnetplumber.net>
Date:	Wed, 5 Jun 2013 08:41:16 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Mike Rapoport <mike.rapoport@...ellosystems.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 03/10] vxlan: move IGMP join/leave to work
 queue

On Wed, 5 Jun 2013 10:29:10 +0300
Mike Rapoport <mike.rapoport@...ellosystems.com> wrote:

> On Wed, Jun 5, 2013 at 9:47 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Wed, 05 Jun 2013 at 04:24 GMT, Stephen Hemminger <stephen@...workplumber.org> wrote:
> >> Do join/leave from work queue to avoid lock inversion problems
> >> between normal socket and RTNL. The code comes out cleaner
> >> as well.
> >>
> >> Uses Cong Wang's suggestion to turn refcnt into a real atomic
> >> since now need to handle case where last use of socket is IGMP
> >> worker.
> >>
> >> Also fixes race where vxlan_stop could be called after
> >> device was deleted on module removal. The call to rtnl_link_unregister
> >> would call dellink while vxlan device was still up. Reordering
> >> the calls fixes it.
> >>
> >
> > After the first 3 patches applied, I got:
> >
> > [   55.010954] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
> > [   55.013309] CPU: 1 PID: 163 Comm: kworker/1:2 Not tainted
> > 3.10.0-rc2+ #1150
> > [   55.013309] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> > [   55.013309] Workqueue: events vxlan_igmp_work
> 
> I think the problem happens because vxlan_dellink does
> unregister_netdevice_queue and then immediately calls
> vxlan_sock_release and thus vs_sock is released before igmp_work
> starts

This is handled because a refcount is acquired before the igmp_work
is scheduled.


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