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From: John Stultz <john.stultz@linaro.org>
Date: Fri, 11 Aug 2017 17:31:44 -0700
Message-ID: <CALAqxLV-e=Uz_zG6VYcKSTG0+qJdpPOv0_vagnGx4bABgzO4tg@mail.gmail.com>
Subject: Re: unregister_netdevice: waiting for eth0 to become free. Usage
 count = 1
To: Wei Wang <weiwan@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>, Martin KaFai Lau <kafai@fb.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        Linux USB List <linux-usb@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Felipe Balbi <felipe.balbi@linux.intel.com>
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On Fri, Aug 11, 2017 at 5:10 PM, Wei Wang <weiwan@google.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.

Do you still want feedback on the previous changes?

thanks
-john