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

[Rafael Aquini <aquini@redhat.com>]

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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