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

[David Ahern]

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....