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

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Date:   Sat, 3 Feb 2018 13:15:05 +0100
From:   Xin Long <lucien.xin@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Dan Streetman <ddstreet@...onical.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        tommi.t.rantala@...ia.com, alexey.kodanev@...cle.com,
        Neil Horman <nhorman@...driver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        linux-sctp@...r.kernel.org
Subject: Re: net: hang in unregister_netdevice: waiting for lo to become free

On Thu, Feb 1, 2018 at 1:49 AM, Xin Long <lucien.xin@...il.com> wrote:
> On Tue, Jan 30, 2018 at 11:59 PM, David Ahern <dsahern@...il.com> 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@...gle.com> 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@...il.com>
>>> 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@...il.com>
>> 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.