From: Andrea Arcangeli <[email protected]> commit: d179e84ba5da1d0024087d1759a2938817a00f3f
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. [[email protected]: split out patch] Signed-off-by: Andrea Arcangeli <[email protected]> Signed-off-by: Mel Gorman <[email protected]> Reviewed-by: Michal Hocko <[email protected]> Reviewed-by: Minchan Kim <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> --- mm/vmscan.c | 16 ++++++++++++++-- 1 files changed, 14 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index cc1470b..37c5038 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1114,8 +1114,20 @@ 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; } -- 1.7.3.4 _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
