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

John Stultz
2017-08-10T01:26:05Z

On Wed, Aug 9, 2017 at 5:36 PM, Wei Wang <weiwan@google.com> wrote:
> On Wed, Aug 9, 2017 at 4:44 PM, John Stultz <john.stultz@linaro.org> wrote:
>> On Wed, Aug 9, 2017 at 4:34 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>> (Cc'ing Wei whose commit was blamed)
>>>
>>> On Mon, Aug 7, 2017 at 2:15 PM, John Stultz <john.stultz@linaro.org> wrote:
>>>> On Mon, Aug 7, 2017 at 2:05 PM, John Stultz <john.stultz@linaro.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