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

From: Dmitry Vyukov <dvyukov@google.com>
To: Xin Long <lucien.xin@gmail.com>
Cc: David Ahern <dsahern@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	David Miller <davem@davemloft.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>,
	Dan Streetman <ddstreet@canonical.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Tommi Rantala <tommi.t.rantala@nokia.com>,
	Alexey Kodanev <alexey.kodanev@oracle.com>,
	Neil Horman <nhorman@tuxdriver.com>,
	Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
	linux-sctp@vger.kernel.org
Subject: Re: net: hang in unregister_netdevice: waiting for lo to become free
Date: Mon, 19 Feb 2018 19:59:43 +0100	[thread overview]
Message-ID: <CACT4Y+aV_v6zNS6Ac1u1cB2GZ7QhjNxBeg0FNabUhrndt5CqZw@mail.gmail.com> (raw)
In-Reply-To: <CADvbK_fKDbUnAkdLrgm6rgj895Gb06AK7HaT0s9VD=zdF+vf6Q@mail.gmail.com>

On Sat, Feb 3, 2018 at 1:15 PM, Xin Long <lucien.xin@gmail.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@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.
>>>>>
>>>>> 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@gmail.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@gmail.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.