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From:   Cong Wang <xiyou.wangcong@gmail.com>
Date:   Tue, 30 Jan 2018 10:32:26 -0800
Message-ID: <CAM_iQpVo0iSXKSR=Qc+7syn77BnhE2R72M2u5YfJF=fBkJHjsw@mail.gmail.com>
Subject: Re: net: hang in unregister_netdevice: waiting for lo to become free
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     David Miller <davem@davemloft.net>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Eric Dumazet <edumazet@google.com>,
        Willem de Bruijn <willemb@google.com>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        syzkaller <syzkaller@googlegroups.com>
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On Tue, Jan 30, 2018 at 4:09 AM, Dmitry Vyukov <dvyukov@google.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.