netdev - Re: unregister_netdevice warnings when deleting netns

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Message-ID: <87mvw54tcu.fsf@x220.int.ebiederm.org>
Date:	Tue, 29 Sep 2015 01:44:49 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Anand Gurram <anandarao.gurram@...il.com>
Cc:	Julian Anastasov <ja@....bg>, NETDEV <netdev@...r.kernel.org>
Subject: Re: unregister_netdevice warnings when deleting netns

Anand Gurram <anandarao.gurram@...il.com> writes:

>>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.
>
> The message just spits out few times and then goes away, I am trying
> to debug why cleanup is taking long,
> and where it is still referenced. Any pointers in debugging such
> issues will be of great help.

The one thing I have done in the past is to instrument dev_hold
and dev_put and look where in the code the stragglers are coming from
(when I can reproduce the issue reliably).

Sometimes people have addressed this class of issue with code review,
but with a slow cleanup you can't catch this by finding a missing
dev_put.

It takes some creativity to find these as people rarely make the same
mistake twice.

Eric
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