Commit d179e84b authored Jun 15, 2011 by Andrea Arcangeli Committed by Linus Torvalds Jun 15, 2011

mm: vmscan: do not use page_count without a page pin



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.

[mgorman@suse.de: split out patch]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7454f4ba

mm/vmscan.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -1124,8 +1124,20 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
		nr_lumpy_dirty++;
		scan++;
		} else {
		/* the page is freed already. */
		if (!page_count(cursor_page))
		/*
		* Check if the page is freed already.
		*
		* We can't use page_count() as that
		* requires compound_head and we don't
		* have a pin on the page here. If a
		* page is tail, we may or may not
		* have isolated the head, so assume
		* it's not free, it'd be tricky to
		* track the head status without a
		* page pin.
		*/
		if (!PageTail(cursor_page) &&
		!atomic_read(&cursor_page->_count))
		continue;
		break;
		}