netdev - Re: sctp netns "unregister_netdevice: waiting for lo to become free. Usage count = 1"

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Date:   Wed, 31 Jan 2018 11:42:24 +0200
From:   Tommi Rantala <tommi.t.rantala@...ia.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     Vlad Yasevich <vyasevich@...il.com>, linux-sctp@...r.kernel.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: sctp netns "unregister_netdevice: waiting for lo to become free.
 Usage count = 1"

On 30.01.2018 23:03, Neil Horman wrote:
> On Tue, Jan 30, 2018 at 09:24:17PM +0200, Tommi Rantala wrote:
>> On 30.01.2018 17:59, Neil Horman wrote:
>>> On Mon, Jan 29, 2018 at 05:55:45PM +0200, Tommi Rantala wrote:
>>>>
>>>> ip netns add TEST
>>>> ip netns exec TEST ip link set lo up
>>>> ip link add dummy0 type dummy
>>>> ip link add dummy1 type dummy
>>>> ip link add dummy2 type dummy
>>>> ip link set dev dummy0 netns TEST
>>>> ip link set dev dummy1 netns TEST
>>>> ip link set dev dummy2 netns TEST
>>>> ip netns exec TEST ip addr add 192.168.1.1/24 dev dummy0
>>>> ip netns exec TEST ip link set dummy0 up
>>>> ip netns exec TEST ip addr add 192.168.1.2/24 dev dummy1
>>>> ip netns exec TEST ip link set dummy1 up
>>>> ip netns exec TEST ip addr add 192.168.1.3/24 dev dummy2
>>>> ip netns exec TEST ip link set dummy2 up
>>>> ip netns exec TEST sctp_test -H 192.168.1.2 -P 20002 -h 192.168.1.1 -p 20000
>>>> -s -B 192.168.1.3
>>>> ip netns del TEST
>>>>
>>> Does the problem occur if you don't set lo up?
>>
>> Still happens after dropping "ip netns exec TEST ip link set lo up".
>>
>> Omitting "-B 192.168.1.3" from the sctp_test args helps.
>>
> Thats....wierd.  I'll look at the sctp_test code in the AM

I think there's a problem in the dst refcounting in sctp_v4_get_dst()

There's a dst_entry struct that has >0 refcnt after running the 
testcase, which makes it impossible to delete the loopback device, as 
that dst is never freed.

I'll try to make a patch.

Tommi