[PATCH v1 7/8] PM / Hibernate: use pfn_to_online_page()

Michal Hocko mhocko at kernel.org
Mon Nov 19 12:13:06 UTC 2018


On Mon 19-11-18 11:16:15, David Hildenbrand wrote:
> Let's use pfn_to_online_page() instead of pfn_to_page() when checking
> for saveable pages to not save/restore offline memory sections.
> 
> Cc: "Rafael J. Wysocki" <rjw at rjwysocki.net>
> Cc: Pavel Machek <pavel at ucw.cz>
> Cc: Len Brown <len.brown at intel.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Matthew Wilcox <willy at infradead.org>
> Cc: Michal Hocko <mhocko at suse.com>
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Suggested-by: Michal Hocko <mhocko at kernel.org>
> Signed-off-by: David Hildenbrand <david at redhat.com>

I have only a very vague understanding of this specific code but I do
not really see any real reason for checking offlined ranges. Also
offline pfn ranges might have uninitialized struct pages so making
any decisions of the struct page is basically undefined behavior.

Acked-by: Michal Hocko <mhocko at suse.com>

> ---
>  kernel/power/snapshot.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 640b2034edd6..87e6dd57819f 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1215,8 +1215,8 @@ static struct page *saveable_highmem_page(struct zone *zone, unsigned long pfn)
>  	if (!pfn_valid(pfn))
>  		return NULL;
>  
> -	page = pfn_to_page(pfn);
> -	if (page_zone(page) != zone)
> +	page = pfn_to_online_page(pfn);
> +	if (!page || page_zone(page) != zone)
>  		return NULL;
>  
>  	BUG_ON(!PageHighMem(page));
> @@ -1277,8 +1277,8 @@ static struct page *saveable_page(struct zone *zone, unsigned long pfn)
>  	if (!pfn_valid(pfn))
>  		return NULL;
>  
> -	page = pfn_to_page(pfn);
> -	if (page_zone(page) != zone)
> +	page = pfn_to_online_page(pfn);
> +	if (!page || page_zone(page) != zone)
>  		return NULL;
>  
>  	BUG_ON(PageHighMem(page));
> -- 
> 2.17.2

-- 
Michal Hocko
SUSE Labs


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