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

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Date:   Tue, 30 Jan 2018 21:08:32 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     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>
Subject: Re: net: hang in unregister_netdevice: waiting for lo to become free

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?