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

[Tommi Rantala]

On 19.02.2018 20:59, Dmitry Vyukov wrote:
> On Sat, Feb 3, 2018 at 1:15 PM, Xin Long <lucien.xin@xxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxx>
> > > > > 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@xxxxxxxxx>
> > > > 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.

These two commits are in v4.16-rc1:

commit 4a31a6b19f9ddf498c81f5c9b089742b7472a6f8
Author: Tommi Rantala <tommi.t.rantala@xxxxxxxxx>
Date:   Mon Feb 5 21:48:14 2018 +0200

    sctp: fix dst refcnt leak in sctp_v4_get_dst
...
    Fixes: 410f03831 ("sctp: add routing output fallback")
    Fixes: 0ca50d12f ("sctp: fix src address selection if using 
secondary addresses")


commit 957d761cf91cdbb175ad7d8f5472336a4d54dbf2
Author: Alexey Kodanev <alexey.kodanev@xxxxxxxxxx>
Date:   Mon Feb 5 15:10:35 2018 +0300

    sctp: fix dst refcnt leak in sctp_v6_get_dst()
...
    Fixes: dbc2b5e9a09e ("sctp: fix src address selection if using 
secondary addresses for ipv6")


I guess we missed something if it's still reproducible.

I can check it later this week, unless someone else beat me to it.

Tommi