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

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Date:	Wed, 19 Mar 2014 23:44:42 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>
Cc:	stephen@...workplumber.org, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: fix RTNL assert fail in DAD

On Wed, Mar 19, 2014 at 01:53:19PM -0400, David Miller wrote:
> From: Stephen Hemminger <stephen@...workplumber.org>
> Date: Tue, 18 Mar 2014 23:58:11 -0700
> 
> > 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.

Exactly, I was afraid of those things (not exactly of TAHI breakage but of
real packet loss in case of late workqueue scheduling).

> >> 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.
> 
> Ok, the timer stuff could run from a workqueue just fine.

We have no-timer invocations, too, like addrconf_prefix_rcv. In that case the
whole handling of the router advertisment should get deferred into the
workqueue.

Bye,

  Hannes

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