Re: net: hang in unregister_netdevice: waiting for lo to become free

[Xin Long]

On Thu, Feb 1, 2018 at 1:49 AM, Xin Long <lucien.xin@xxxxxxxxx> wrote:
> On Tue, Jan 30, 2018 at 11:59 PM, David Ahern <dsahern@xxxxxxxxx> wrote:
>> On 1/30/18 1:57 PM, David Ahern wrote:
>>> On 1/30/18 1:08 PM, Daniel Borkmann wrote:
>>>> On 01/30/2018 07:32 PM, Cong Wang wrote:
>>>>> On Tue, Jan 30, 2018 at 4:09 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>>>>> Hello,
>>>>>>
>>>>>> The following program creates a hang in unregister_netdevice.
>>>>>> cleanup_net work hangs there forever periodically printing
>>>>>> "unregister_netdevice: waiting for lo to become free. Usage count = 3"
>>>>>> and creation of any new network namespaces hangs forever.
>>>>>
>>>>> Interestingly, this is not reproducible on net-next.
>>>>
>>>> The most recent change on netns refcnt was 4ee806d51176 ("net: tcp: close
>>>> sock if net namespace is exiting") in net/net-next from 5 days ago, maybe
>>>> fixed due to that?
>>>>
>>>
>>> This appears to be the commit introducing the refcnt leak:
>>>
>>> $ git bisect bad
>>> dbc2b5e9a09e9a6664679a667ff81cff6e5f2641 is the first bad commit
>>> commit dbc2b5e9a09e9a6664679a667ff81cff6e5f2641
>>> Author: Xin Long <lucien.xin@xxxxxxxxx>
>>> Date:   Fri May 12 14:39:52 2017 +0800
>>>
>>>     sctp: fix src address selection if using secondary addresses for ipv6
>>>
>>>
>>> v4.14 is bad. Running bisect in the background while doing other things....
>>>
>>
>> Interesting. The commit that avoids the refcnt leak is
>>
>> commit 955ec4cb3b54c7c389a9f830be7d3ae2056b9212
>> Author: David Ahern <dsahern@xxxxxxxxx>
>> Date:   Wed Jan 24 19:45:29 2018 -0800
>>
>>     net/ipv6: Do not allow route add with a device that is down
>>
>> That commit does not intentionally address the problem so it is just
>> masking the problematic code introduced by the commit above.
> Thanks, David A.
>
> I'm still on a trip. will look into this asap.

Alexey and Tommi already had the patches for this issue on
both SCTP v4 and v6 dst_get, Thanks.