netdev - Re: [PATCH net] ipv6: fix RTNL assert fail in DAD

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Message-ID: <20140318235811.0d8f230a@nehalam.linuxnetplumber.net>
Date:	Tue, 18 Mar 2014 23:58:11 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	David Miller <davem@...emloft.net>
Cc:	hannes@...essinduktion.org, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: fix RTNL assert fail in DAD

On Wed, 19 Mar 2014 00:17:36 -0400 (EDT)
David Miller <davem@...emloft.net> wrote:

> From: Stephen Hemminger <stephen@...workplumber.org>
> Date: Tue, 18 Mar 2014 17:54:06 -0700
> 
> > On Tue, 18 Mar 2014 01:29:08 +0100
> > Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:
> > 
> >> I wonder if we should put the whole ipv6_ifa_notify infrastructure in a
> >> workqueue? I don't like that either and it could add subtile races.
> > 
> > That is option, might be some call chains that already have rtnl_lock held.
> 
> There are TAHI ipv6 conformance tests that expect state changes to be
> precisely synchronous.
> 
> And frankly it's pretty reasonable to send two packets back to back,
> one which causes the state change and one which tests if the state
> change happened, and expect that to work.

It is more the timer based state changes that are problematic because
they aren't acquire RTNL.
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