netdev - Re: [PATCH 1/3] ipv6: make inet6addr_chain blocking and always call with rtnl locked

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Message-Id: <20150516.172214.820543928532454603.davem@davemloft.net>
Date:	Sat, 16 May 2015 17:22:14 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	khlebnikov@...dex-team.ru
Cc:	netdev@...r.kernel.org, maheshb@...gle.com, jbenc@...hat.com,
	hannes@...essinduktion.org
Subject: Re: [PATCH 1/3] ipv6: make inet6addr_chain blocking and always
 call with rtnl locked

From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Date: Thu, 14 May 2015 16:56:18 +0300

> Unlike to inetaddr_chain inet6addr_chain is atomic and called from bh
> context without rtnl when ipv6 receives router advertisement packet.
> 
> Several drivers don't know about that: ipvlan thinks that it has rtnl
> here, ocrdma locks mutex inside callback. Probably there is more.
> 
> This patch makes it blocking and calls from first stage of DAD work.
> Looks like this is completely safe and rtnl already locked here.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

I don't see how you can make the inet6addr_chain blocking when it is
invoked from software interrupt context.

You also cannot try to defer these operations to a workqueue or
similar to get into a blockable context, because various ipv6
testsuites depend upon the addressing state change happening
when we process the packet that triggers that change.

Instead, I think you have to make the users of inet6addr_chain
aware of the context in which they execute.

Thanks.
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