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From: John Stultz <john.stultz@linaro.org>
Date: Fri, 11 Aug 2017 20:07:52 -0700
Message-ID: <CALAqxLX=GP5FMXfoEGuSwUuZp0cTyUCzh+ntSdknevjJioM0hg@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 5:31 PM, John Stultz <john.stultz@linaro.org> wrote:
> 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.

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@linaro.org>

thanks again
-john