netdev - Re: [PATCH v2] vxlan: remove the redundant gro_cells

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Date:   Fri, 15 Mar 2019 22:08:41 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>, liuzhiqiang26@...wei.com,
        petrm@...lanox.com, idosch@...lanox.com, sd@...asysnail.net,
        mousuanming@...wei.com, netdev@...r.kernel.org,
        mingfangsen@...wei.com, zhoukang7@...wei.com,
        wangxiaogang3@...wei.com
Subject: Re: [PATCH v2] vxlan: remove the redundant gro_cells_destroy()
 calling.

On Fri, 15 Mar 2019 11:56:01 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> On 03/15/2019 11:02 AM, David Miller wrote:
> > From: Eric Dumazet <eric.dumazet@...il.com>
> > Date: Fri, 15 Mar 2019 09:06:25 -0700
> >   
> >>
> >>
> >> On 03/15/2019 08:28 AM, Stefano Brivio wrote:  
> >>> On Fri, 15 Mar 2019 23:18:52 +0800
> >>> Zhiqiang Liu <liuzhiqiang26@...wei.com> wrote:
> >>>  
> >>>> In vxlan_destroy_tunnels func, unregister_netdevice_queue is called after
> >>>> gro_cells_destroy func. However, in unregister_netdevice_queue func, the
> >>>> gro_cells_destroy func will also call the gro_cells_destroy func as the
> >>>> following routine:
> >>>> unregister_netdevice_many() -> rollback_registered_many()  
> >>>> -> ndo_uninit() -> gro_cells_destroy()    
> >>>>
> >>>> Signed-off-by: Suanming.Mou <mousuanming@...wei.com>
> >>>> Reviewed-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
> >>>> Reviewed-by: Stefano Brivio <sbrivio@...hat.com>  
> >>>
> >>> NACK, please read my and Eric's comments to v1 -- giving me more than 23
> >>> minutes to answer would have been a nice touch as well :)
> >>>  
> >>
> >> Sorry for the confusion, I forgot to add the question marks to my sentences.
> >>
> >> In fact, this is a bug fix, that we missed in the previous fix.
> >>
> >> Technically the bug is older.  
> > 
> > Please elaborate.
> >   
> 
> Commit ad6c9986bcb62
> ("vxlan: Fix GRO cells race condition between receive and link delete")
> 
> fixed a race condition for the typical case a vxlan device is dismantled from the
> current netns.
> 
> But if a netns is dismantled, we call vxlan_destroy_tunnels()
> to schedule a unregister_netdevice_queue() of all the vxlan tunnels
> that are related to this netns.

Won't that happen via ops_exit_list() only after synchronize_rcu() is
called by cleanup_net(), though? Is there another path I missed?

-- 
Stefano