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Subject[092/129] memory hotplug: fix next block calculation in is_removable
2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

commit 0dcc48c15f63ee86c2fcd33968b08d651f0360a5 upstream.

next_active_pageblock() is for finding next _used_ freeblock. It skips
several blocks when it finds there are a chunk of free pages lager than
pageblock. But it has 2 bugs.

1. We have no lock. page_order(page) - pageblock_order can be minus.
2. pageblocks_stride += is wrong. it should skip page_order(p) of pages.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
mm/memory_hotplug.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -584,19 +584,19 @@ static inline int pageblock_free(struct
/* Return the start of the next active pageblock after a given page */
static struct page *next_active_pageblock(struct page *page)
{
- int pageblocks_stride;
-
/* Ensure the starting page is pageblock-aligned */
BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1));

- /* Move forward by at least 1 * pageblock_nr_pages */
- pageblocks_stride = 1;
-
/* If the entire pageblock is free, move to the end of free page */
- if (pageblock_free(page))
- pageblocks_stride += page_order(page) - pageblock_order;
+ if (pageblock_free(page)) {
+ int order;
+ /* be careful. we don't have locks, page_order can be changed.*/
+ order = page_order(page);
+ if ((order < MAX_ORDER) && (order >= pageblock_order))
+ return page + (1 << order);
+ }

- return page + (pageblocks_stride * pageblock_nr_pages);
+ return page + pageblock_nr_pages;
}

/* Checks if this range of memory is likely to be hot-removable. */



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