mm: strictly require elevated page refcount in isolate_lru_page()
isolate_lru_page() must be called only with stable reference to the page,
this is what is written in the comment above it, this is reasonable.
current isolate_lru_page() users and its page extra reference sources:
mm/huge_memory.c:
__collapse_huge_page_isolate() - reference from pte
mm/memcontrol.c:
mem_cgroup_move_parent() - get_page_unless_zero()
mem_cgroup_move_charge_pte_range() - reference from pte
mm/memory-failure.c:
soft_offline_page() - fixed, reference from get_any_page()
delete_from_lru_cache() - reference from caller or get_page_unless_zero()
[ seems like there bug, because __memory_failure() can call
page_action() for hpages tail, but it is ok for
isolate_lru_page(), tail getted and not in lru]
mm/memory_hotplug.c:
do_migrate_range() - fixed, get_page_unless_zero()
mm/mempolicy.c:
migrate_page_add() - reference from pte
mm/migrate.c:
do_move_page_to_node_array() - reference from follow_page()
mlock.c: - various external references
mm/vmscan.c:
putback_lru_page() - reference from isolate_lru_page()
It seems that all isolate_lru_page() users are ready now for this
restriction. So, let's replace redundant get_page_unless_zero() with
get_page() and add page initial reference count check with VM_BUG_ON()
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d303b60..890f541 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1207,13 +1207,16 @@
{
int ret = -EBUSY;
+ VM_BUG_ON(!page_count(page));
+
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
spin_lock_irq(&zone->lru_lock);
- if (PageLRU(page) && get_page_unless_zero(page)) {
+ if (PageLRU(page)) {
int lru = page_lru(page);
ret = 0;
+ get_page(page);
ClearPageLRU(page);
del_page_from_lru_list(zone, page, lru);