netdev - Re: 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:   Wed, 25 Apr 2018 16:16:07 +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>,
        Dan Streetman <ddstreet@...e.org>,
        Dan Streetman <ddstreet@...onical.com>
Subject: Re: Repeating "unregister_netdevice: waiting for lo to become free"
 caused by upstream 76da0704507bb ("ipv6: only call ip6_route_dev_notify()
 once for NETDEV_UNREGISTER")

On 23.04.2018 15:08, Rafał Miłecki wrote:
> 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/

Today I tried 4.14.34 to see if that helps. Unfortunately it doesn't. I
still experience the same problem.

 From reading various reports regarding that "unregister_netdevice:
waiting for lo to become free" message it appears the problem is caused
by a leaking dst refcnt somewhere in the kernel code.

I found links to few commit fixing leaks at various places:
4a31a6b19f9dd ("sctp: fix dst refcnt leak in sctp_v4_get_dst")
957d761cf91cd ("sctp: fix dst refcnt leak in sctp_v6_get_dst()")
4ee806d51176b ("net: tcp: close sock if net namespace is exiting")
d747a7a51b009 ("tcp: reset sk_rx_dst in tcp_disconnect()")
751eb6b6042a5 ("ipv6: addrconf: fix dev refcont leak when DAD failed")

All above patches are present in the linux-v4.4.y and are part of kernel
4.4.124 I use. So it seems I'm facing yet another dst refcnt leak.

Could commit 2417da3f4d6bc ("ipv6: only call ip6_route_dev_notify() once
for NETDEV_UNREGISTER") introduce a new dst refcnt leak? Or does it only
expost existing one?