netdev - Re: unregister_netdevice warnings when deleting netns

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Message-ID: <alpine.LFD.2.11.1509290858500.2072@ja.home.ssi.bg>
Date:	Tue, 29 Sep 2015 09:03:40 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Anand Gurram <anandarao.gurram@...il.com>,
	NETDEV <netdev@...r.kernel.org>
Subject: Re: unregister_netdevice warnings when deleting netns


	Hello,

On Mon, 28 Sep 2015, Eric W. Biederman wrote:

> Julian Anastasov <ja@....bg> writes:
> 
> > On Mon, 28 Sep 2015, Anand Gurram wrote:
> >
> >> I am currently using kernel version 3.16.7 on a linux switch.
> >> While creating and destroying network namespaces I am observing below logs
> >> on the console
> >> "unregister_netdevice: waiting for lo to become free. Usage count = 1"
> >> 
> >> Can you please suggest and provide instructions on how to debug this issue.
> >> If any fix already available can you please point me to the link.
> >
> > 	There are two commits from Linux 4.2 that may help:
> >
> > commit e9e4dd3267d0 ("net: do not process device backlog during unregistration")
> > commit 2c17d27c36dc ("net: call rcu_read_lock early in process_backlog")
> >
> If that message repeats indefinitely it means there is a leaked
> reference to the network namespaces lo device.
> 
> If the message just spits out a few times and then goes away it simply
> means that something is taking a while to cleanup and drop it's
> reference.
> 
> This is slightly complicated by the fact that it is not uncommon when a
> network device goes away to redirect all references to itself to the lo
> device.

	Yes, there is a little chance with forwarding disabled,
i.e. when presence of "ipv4: Avoid crashing in ip_error" does
not matter, flying packet to leave new reference somewhere,
without crashing. But it may be another problem, of course.

Regards

--
Julian Anastasov <ja@....bg>
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