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

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Message-ID: <5973966e-fcd9-7ee5-a9c4-b79d22c1b9dd@nokia.com>
Date:   Tue, 20 Feb 2018 09:56:38 +0200
From:   Tommi Rantala <tommi.t.rantala@...ia.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>, Xin Long <lucien.xin@...il.com>
Cc:     David Ahern <dsahern@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Cong Wang <xiyou.wangcong@...il.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>,
        Alexey Kodanev <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 19.02.2018 20:59, Dmitry Vyukov wrote:
> On Sat, Feb 3, 2018 at 1:15 PM, Xin Long <lucien.xin@...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.
> 
> 
> 
> Is this meant to be fixed already? I am still seeing this on the
> latest upstream tree.
> 

These two commits are in v4.16-rc1:

commit 4a31a6b19f9ddf498c81f5c9b089742b7472a6f8
Author: Tommi Rantala <tommi.t.rantala@...ia.com>
Date:   Mon Feb 5 21:48:14 2018 +0200

     sctp: fix dst refcnt leak in sctp_v4_get_dst
...
     Fixes: 410f03831 ("sctp: add routing output fallback")
     Fixes: 0ca50d12f ("sctp: fix src address selection if using 
secondary addresses")


commit 957d761cf91cdbb175ad7d8f5472336a4d54dbf2
Author: Alexey Kodanev <alexey.kodanev@...cle.com>
Date:   Mon Feb 5 15:10:35 2018 +0300

     sctp: fix dst refcnt leak in sctp_v6_get_dst()
...
     Fixes: dbc2b5e9a09e ("sctp: fix src address selection if using 
secondary addresses for ipv6")


I guess we missed something if it's still reproducible.

I can check it later this week, unless someone else beat me to it.

Tommi