mm: migrate: don't rely on __PageMovable() of newpage after unlocking it
We had a race in the old balloon compaction code before b1123ea6d3
("mm: balloon: use general non-lru movable page feature") refactored it
that became visible after backporting 195a8c43e9 ("virtio-balloon:
deflate via a page list") without the refactoring.
The bug existed from commit d6d86c0a7f ("mm/balloon_compaction:
redesign ballooned pages management") till b1123ea6d3 ("mm: balloon:
use general non-lru movable page feature"). d6d86c0a7f
("mm/balloon_compaction: redesign ballooned pages management") was
backported to 3.12, so the broken kernels are stable kernels [3.12 -
There was a subtle race between dropping the page lock of the newpage in
__unmap_and_move() and checking for __is_movable_balloon_page(newpage).
Just after dropping this page lock, virtio-balloon could go ahead and
deflate the newpage, effectively dequeueing it and clearing PageBalloon,
in turn making __is_movable_balloon_page(newpage) fail.
This resulted in dropping the reference of the newpage via
putback_lru_page(newpage) instead of put_page(newpage), leading to
page->lru getting modified and a !LRU page ending up in the LRU lists.
With 195a8c43e9 ("virtio-balloon: deflate via a page list")
backported, one would suddenly get corrupted lists in
- WARNING: CPU: 13 PID: 6586 at lib/list_debug.c:59 __list_del_entry+0xa1/0xd0
- list_del corruption. prev->next should be ffffe25396, but was dead000000
Nowadays this race is no longer possible, but it is hidden behind very
ugly handling of __ClearPageMovable() and __PageMovable().
__ClearPageMovable() will not make __PageMovable() fail, only
PageMovable(). So the new check (__PageMovable(newpage)) will still
hold even after newpage was dequeued by virtio-balloon.
If anybody would ever change that special handling, the BUG would be
introduced again. So instead, make it explicit and use the information
of the original isolated page before migration.
This patch can be backported fairly easy to stable kernels (in contrast
to the refactoring).
Fixes: d6d86c0a7f ("mm/balloon_compaction: redesign ballooned pages management")
Signed-off-by: David Hildenbrand <email@example.com>
Reported-by: Vratislav Bendel <firstname.lastname@example.org>
Acked-by: Michal Hocko <email@example.com>
Acked-by: Rafael Aquini <firstname.lastname@example.org>
Cc: Mel Gorman <email@example.com>
Cc: "Kirill A. Shutemov" <firstname.lastname@example.org>
Cc: Michal Hocko <email@example.com>
Cc: Naoya Horiguchi <firstname.lastname@example.org>
Cc: Jan Kara <email@example.com>
Cc: Andrea Arcangeli <firstname.lastname@example.org>
Cc: Dominik Brodowski <email@example.com>
Cc: Matthew Wilcox <firstname.lastname@example.org>
Cc: Vratislav Bendel <email@example.com>
Cc: Rafael Aquini <firstname.lastname@example.org>
Cc: Konstantin Khlebnikov <email@example.com>
Cc: Minchan Kim <firstname.lastname@example.org>
Cc: <email@example.com> [3.12 - 4.7]
Signed-off-by: Andrew Morton <firstname.lastname@example.org>
Signed-off-by: Linus Torvalds <email@example.com>