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

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Message-ID: <20180131123105.GB23692@hmswarspite.think-freely.org>
Date:   Wed, 31 Jan 2018 07:31:05 -0500
From:   Neil Horman <nhorman@...driver.com>
To:     Tommi Rantala <tommi.t.rantala@...ia.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 Wed, Jan 31, 2018 at 11:42:24AM +0200, Tommi Rantala wrote:
> 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.
> 
Are you looking at the second for loop there, which uses ip_route_output_key,
but discards the result if dst is already set?  That does look a bit wonky, and
the same problem may exist in the ipv6 path.  Let me know what the result is.
Neil

> Tommi
> 
>