linux-kernel - Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply rcu_access

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Date:	Wed, 9 Oct 2013 17:28:33 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, sbw@....edu,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply
 rcu_access_pointer() to avoid sparse false positive

On Wed, Oct 09, 2013 at 05:12:40PM -0700, Eric Dumazet wrote:
> On Wed, 2013-10-09 at 16:40 -0700, Josh Triplett wrote:
> 
> > that.  Constructs like list_del_rcu are much clearer, and not
> > open-coded.  Open-coding synchronization code is almost always a Bad
> > Idea.
> 
> OK, so you think there is synchronization code.
> 
> I will shut up then, no need to waste time.

As you said earlier, we should at least get rid of the memory barrier
as long as we are changing the code.

Josh, what would you suggest as the best way to avoid the memory barrier,
keep sparse happy, and not be too ugly?

							Thanx, Paul

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