linux-kernel - Re: [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations

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Date:	Tue, 15 Jul 2014 09:06:00 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>,
	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] percpu: add data dependency barrier in percpu
 accessors and operations

On Tue, 15 Jul 2014, Paul E. McKenney wrote:

> If I understand your initialization procedure correctly, you need at least
> an smp_wmb() on the update side and at least an smp_read_barrier_depends()
> on the read side.

A barrier for data that is not in the cache of the read side? That has
not been accessed yet (well there could have been a free_percpu before but
if so then the cache line was evicted by the initialization code).


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