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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net] ipv6: fix RTNL assert fail in DAD
Date: Wed, 19 Mar 2014 00:17:36 -0400 (EDT)
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From: Stephen Hemminger <stephen@networkplumber.org>
Date: Tue, 18 Mar 2014 17:54:06 -0700

> On Tue, 18 Mar 2014 01:29:08 +0100
> Hannes Frederic Sowa <hannes@stressinduktion.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.