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mm: do not use page_count() without a page pin 

d179e84ba ("mm: vmscan: do not use page_count without a page pin") fixed
this problem in vmscan.c but same problem is in __count_immobile_pages().

I copy and paste d179e84ba's contents for description.

"It is unsafe to run page_count during the physical pfn scan because
compound_head could trip on a dangling pointer when reading
page->first_page if the compound page is being freed by another CPU."

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Wanpeng Li <liwp.linux@gmail.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Minchan Kim 2012-07-31 16:42:59 -07:00 committed by Linus Torvalds
parent de34d965a8
commit 97d255c816
1 changed files with 8 additions and 1 deletions
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9
mm/page_alloc.c
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@ -5500,11 +5500,18 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
continue;
page = pfn_to_page(check);
if (!page_count(page)) {
/*
* We can't use page_count without pin a page
* because another CPU can free compound page.
* This check already skips compound tails of THP
* because their page->_count is zero at all time.
*/
if (!atomic_read(&page->_count)) {
if (PageBuddy(page))
iter += (1 << page_order(page)) - 1;
continue;
}
if (!PageLRU(page))
found++;
/*