linux-kernel - Re: unregister_netdevice: waiting for eth0 to become free. Usage count = 1

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Message-ID: <CAEA6p_DO31cGhe=mdd7yOFLJVt+Ys2JwxQHLkjOX9zZEpqCmJw@mail.gmail.com>
Date:   Sat, 12 Aug 2017 12:29:17 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>
Subject: Re: unregister_netdevice: waiting for eth0 to become free. Usage
 count = 1

> Looks good so far! I've not hit the issue yet.
>

Great. I will prepare an official patch then.

> Thanks so much for sorting out a fix!
>
> If its useful:
> Tested-by: John Stultz <john.stultz@...aro.org>

Sure will do.

Thanks.
Wei

On Fri, Aug 11, 2017 at 8:07 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Fri, Aug 11, 2017 at 5:31 PM, John Stultz <john.stultz@...aro.org> wrote:
>> On Fri, Aug 11, 2017 at 5:10 PM, Wei Wang <weiwan@...gle.com> wrote:
>>>> If after Cong's fix, the issue still happens, could you help try the
>>>> patch attached and collect all logs when you try the reproduce the
>>>> issue? It would be great to have logs for both success case and the
>>>> failure case.
>>>>
>>>> Thanks so much for your help.
>>>>
>>>
>>> I think we have a potential fix for this issue.
>>> Martin and I found that when addrconf_dst_alloc() creates a rt6, it is
>>> possible that rt6->dst.dev points to loopback device while
>>> rt6->rt6i_idev->dev points to a real device.
>>> When the real device goes down, the current fib6 clean up code only
>>> checks for rt6->dst.dev and assumes rt6->rt6i_idev->dev is the same.
>>> That leaves unreleased refcnt on the real device if rt6->dst.dev
>>> points to loopback dev.
>>>
>>> The attached potential fix is tested by Martin and made sure it fixes his issue.
>>>
>>> John,
>>> It will be great if you can also give it a try and see if it fixes the
>>> issue on your side before I submit an official patch.
>>
>> So yes, sorry I haven't been able to get back quicker on the other
>> patches sent, was mucking about in other work.
>>
>> So yea, this patch  (potential fix for unregister_netdevice()) seems
>> to avoid the issue.
>>
>> I'm going to do some further testing, but its looking good so far.
>
> Looks good so far! I've not hit the issue yet.
>
> Thanks so much for sorting out a fix!
>
> If its useful:
> Tested-by: John Stultz <john.stultz@...aro.org>
>
> thanks again
> -john