netdev - Repeating "unregister_netdevice: waiting for lo to become free" caused by upstream 76da0704507bb ("ipv6: only call ip6_route_dev_notify() once for NETDEV

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Date:   Mon, 23 Apr 2018 15:08:08 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     WANG Cong <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Network Development <netdev@...r.kernel.org>,
        jeffy <jeffy.chen@...k-chips.com>,
        David Ahern <dsahern@...il.com>,
        Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stable <stable@...r.kernel.org>
Subject: Repeating "unregister_netdevice: waiting for lo to become free"
 caused by upstream 76da0704507bb ("ipv6: only call ip6_route_dev_notify()
 once for NETDEV_UNREGISTER")

Hi,

I've just updated my kernel 4.4.x and noticed a regression. Bisecting
pointed me to the commit 2417da3f4d6bc ("ipv6: only call
ip6_route_dev_notify() once for NETDEV_UNREGISTER") [0] which is
backport of upstream 76da0704507bb. That backported commit has
appeared in a 4.4.103.

I use OpenWrt/LEDE [1] distribution and LXC [2] 1.1.5. After stopping
a container I start getting these messages:
[  229.419188] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  239.660408] unregister_netdevice: waiting for lo to become free.
Usage count = 1
[  249.839189] unregister_netdevice: waiting for lo to become free.
Usage count = 1
(...)

Trying to start LXC nevertheless results in lxc-start command hang
around network configuration. Trying to query LXC state afterwards
results in a lxc-info command hang too.

I tried Googling for this issue and found similar reports:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1729637
https://github.com/fnproject/fn/issues/686
https://lime-technology.com/forums/topic/66863-kernelunregister_netdevice-waiting-for-lo-to-become-free-usage-count-1/
all of them related to the Docker, which is probably a similar use
case to the LXC.

I couldn't find any reference to commit 76da0704507bb that could
suggest fixing the problem I'm seeing.

Does anyone have an idea what is the issue I'm seeing about? Or even
better, how to fix it? Can I provide any additional info that would
help?

[0] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-4.4.y&id=2417da3f4d6bc4fc6c77f613f0e2264090892aa5
[1] https://openwrt.org/
[2] https://linuxcontainers.org/

-- 
Rafał