linux-kernel - Re: [PATCH v8 1/5] mm: introduce a common interface for balloon pages mobility

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Message-ID: <1345562411.23018.111.camel@twins>
Date:	Tue, 21 Aug 2012 17:20:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>,
	paulmck <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v8 1/5] mm: introduce a common interface for balloon
 pages mobility

On Tue, 2012-08-21 at 09:47 -0300, Rafael Aquini wrote:
> +       mapping = rcu_access_pointer(page->mapping);
> +       if (mapping)
> +               mapping = mapping->assoc_mapping; 

The comment near rcu_access_pointer() explicitly says:

 * Return the value of the specified RCU-protected pointer, but omit the
 * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
 * when the value of this pointer is accessed, but the pointer is not
 * dereferenced,

Yet you dereference the pointer... smells like fail to me.
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