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

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Date:   Wed, 9 Aug 2017 22:41:00 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Cong Wang <xiyou.wangcong@...il.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

Hi John,

Is it possible to try the attached patch?
I am not sure if it actually fixes the issue. But I think it is worth a try.
Also, could you get me all the ipv6 routes when you plug in the usb
using "ip -6 route show"? (If you have multiple routing tables
configured, could you dump them all?)

Thanks a lot.
Wei

On Wed, Aug 9, 2017 at 6:36 PM, Wei Wang <weiwan@...gle.com> wrote:
> On Wed, Aug 9, 2017 at 6:26 PM, John Stultz <john.stultz@...aro.org> wrote:
>> On Wed, Aug 9, 2017 at 5:36 PM, Wei Wang <weiwan@...gle.com> wrote:
>>> On Wed, Aug 9, 2017 at 4:44 PM, John Stultz <john.stultz@...aro.org> wrote:
>>>> On Wed, Aug 9, 2017 at 4:34 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>>>> (Cc'ing Wei whose commit was blamed)
>>>>>
>>>>> On Mon, Aug 7, 2017 at 2:15 PM, John Stultz <john.stultz@...aro.org> wrote:
>>>>>> On Mon, Aug 7, 2017 at 2:05 PM, John Stultz <john.stultz@...aro.org> wrote:
>>>>>>> So, with recent testing with my HiKey board, I've been noticing some
>>>>>>> quirky behavior with my USB eth adapter.
>>>>>>>
>>>>>>> Basically, pluging the usb eth adapter in and then removing it, when
>>>>>>> plugging it back in I often find that its not detected, and the system
>>>>>>> slowly spits out the following message over and over:
>>>>>>>   unregister_netdevice: waiting for eth0 to become free. Usage count = 1
>>>>>>
>>>>>> The other bit is that after this starts printing, the board will no
>>>>>> longer reboot (it hangs continuing to occasionally print the above
>>>>>> message), and I have to manually reset the device.
>>>>>>
>>>>>
>>>>> So this warning is not temporarily shown but lasts until a reboot,
>>>>> right? If so it is a dst refcnt leak.
>>>>
>>>> Correct, once I get into the state it lasts until a reboot.
>>>>
>>>>> How reproducible is it for you? From my reading, it seems always
>>>>> reproduced when you unplug and plug your usb eth interface?
>>>>> Is there anything else involved? For example, network namespace.
>>>>
>>>> So with 4.13-rc3/4 I seem to trigger it easily, often with the first
>>>> unplug of the USB eth adapter.
>>>>
>>>> But as I get back closer to 4.12, it seemingly becomes harder to
>>>> trigger, but sometimes still happens.
>>>>
>>>> So far, I've not been able to trigger it with 4.12.
>>>>
>>>> I don't think network namespaces are involved?  Though its out of my
>>>> area, so AOSP may be using them these days.  Is there a simple way to
>>>> check?
>>>>
>>>> I'll also do another bisection to see if the bad point moves back any further.
>>
>> So I went through another bisection around and got  9514528d92d4 ipv6:
>> call dst_dev_put() properly as the first bad commit again.
>>
>>> If you see the problem starts to happen on commit
>>> 9514528d92d4cbe086499322370155ed69f5d06c, could you try reverting all
>>> the following commits:
>>> (from new to old)
>>> 1eb04e7c9e63 net: reorder all the dst flags
>>> a4c2fd7f7891 net: remove DST_NOCACHE flag
>>> b2a9c0ed75a3 net: remove DST_NOGC flag
>>> 5b7c9a8ff828 net: remove dst gc related code
>>> db916649b5dd ipv6: get rid of icmp6 dst garbage collector
>>> 587fea741134 ipv6: mark DST_NOGC and remove the operation of dst_free()
>>> ad65a2f05695 ipv6: call dst_hold_safe() properly
>>> 9514528d92d4 ipv6: call dst_dev_put() properly
>>
>>
>> And reverting this set off of 4.13-rc4 seems to make the issue go away.
>>
>> Is there anything I can test to help narrow down the specific problem
>> with that patchset?
>>
>
> Thanks John for confirming.
> Let me spend some time on the commits and I will let you know if I
> have some debug image for you to try.
>
> Wei
>
>
>> thanks
>> -john

View attachment "0001-ipv6-unregister-netdev-bug-fix.patch" of type "text/x-patch" (3300 bytes)