linux-kernel - Re: [PATCH v2 tip/core/rcu 03/11] rcu: Move smp_mb() from rcu_seq_snap() to rcu_exp_gp_seq

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Message-ID: <20151210204121.GK28602@linux.vnet.ibm.com>
Date:	Thu, 10 Dec 2015 12:41:21 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v2 tip/core/rcu 03/11] rcu: Move smp_mb() from
 rcu_seq_snap() to rcu_exp_gp_seq_snap()

On Thu, Dec 10, 2015 at 09:29:39PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 09, 2015 at 03:03:00PM -0800, Paul E. McKenney wrote:
> > The memory barrier in rcu_seq_snap() is needed only for grace periods,
> > so this commit moves it to the grace-period-oriented wrapper
> > rcu_exp_gp_seq_snap().
> 
> This is a bit short for a memory barrier changelog. I think I remember
> enough of the code to see this is indeed so, but who knows who will
> remember what in another few weeks :-)

;-)

Would it help to add something like the following?

	This change does not add or remove a memory barrier, but instead
	associates it with the right level of abstraction.

							Thanx, Paul

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