linux-kernel - Re: [PATCH v5 1/3] mm: introduce compaction and migration for virtio ballooned pages

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Message-ID: <20120806192418.GB3968@t510.redhat.com>
Date:	Mon, 6 Aug 2012 16:24:18 -0300
From:	Rafael Aquini <aquini@...hat.com>
To:	Rik van Riel <riel@...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>, 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>
Subject: Re: [PATCH v5 1/3] mm: introduce compaction and migration for virtio
 ballooned pages

On Mon, Aug 06, 2012 at 03:06:49PM -0400, Rik van Riel wrote:
> 
> Just a plain rename would work.
>
Ok, I will rename it.
 
> >+static inline bool is_balloon_page(struct page *page)
> >+{
> >+	return (page->mapping && page->mapping == balloon_mapping);
> >+}
> 
> As an aside, since you are only comparing page->mapping and
> not dereferencing it, it can be simplified to just:
> 
> 	return (page->mapping == balloon_mapping);
> 
We really need both comparisons to avoid potential NULL pointer dereferences at
__isolate_balloon_page() & __putback_balloon_page() while running at bare metal
with no balloon driver loaded, since balloon_mapping itself is a pointer which
each balloon driver can set to its own structure. 

Thanks, Rik, for taking the time to look at this patch and provide (always)
valuable feedback.

I'll shortly respin a v6 with your suggestions.

-- Rafael
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