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SubjectRe: [PATCH 1/2] mm: page_isolation: check pfn validity before access
On Thu 06-11-14 16:08:02, Weijie Yang wrote:
> In the undo path of start_isolate_page_range(), we need to check
> the pfn validity before access its page, or it will trigger an
> addressing exception if there is hole in the zone.

This looks a bit fishy to me. I am not familiar with the code much but
at least __offline_pages zone = page_zone(pfn_to_page(start_pfn)) so it
would blow up before we got here. Same applies to the other caller
alloc_contig_range. So either both need a fix and then
start_isolate_page_range doesn't need more checks or this is all
unnecessary.

Please do not make this code more obfuscated than it is already...

> Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
> ---
> mm/page_isolation.c | 7 +++++--
> 1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index d1473b2..3ddc8b3 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -137,8 +137,11 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> undo:
> for (pfn = start_pfn;
> pfn < undo_pfn;
> - pfn += pageblock_nr_pages)
> - unset_migratetype_isolate(pfn_to_page(pfn), migratetype);
> + pfn += pageblock_nr_pages) {
> + page = __first_valid_page(pfn, pageblock_nr_pages);
> + if (page)
> + unset_migratetype_isolate(page, migratetype);
> + }
>
> return -EBUSY;
> }
> --
> 1.7.0.4
>
>
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--
Michal Hocko
SUSE Labs


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