Commit 97d255c8 authored Jul 31, 2012 by Minchan Kim Committed by Linus Torvalds Jul 31, 2012

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



d179e84b ("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 d179e84b'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>

parent de34d965

mm/page_alloc.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -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++;
		/*