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

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Date:   Wed, 9 Aug 2017 17:36:54 -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

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.
>
> thanks
> -john

Hi John,

Does your USB adapter get an IPv6 address?

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 try if it starts to work?

By only reverting 9514528d92d4 definitely won't work as all the later
commits depend on this one.

Thanks a lot.
Wei