For compound pages which are at least order-2 (and hence have a
deferred_list), initialise it and then we can check at free that the
page is not part of a deferred list. We recently found this useful to
rule out a source of corruption.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
mm/huge_memory.c | 2 --
mm/internal.h | 2 ++
mm/memcontrol.c | 2 ++
mm/page_alloc.c | 9 +++++----
4 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9859aa4f7553..04fb994a7b0b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -792,8 +792,6 @@ void folio_prep_large_rmappable(struct folio *folio)
{
if (!folio || !folio_test_large(folio))
return;
- if (folio_order(folio) > 1)
- INIT_LIST_HEAD(&folio->_deferred_list);
folio_set_large_rmappable(folio);
}
diff --git a/mm/internal.h b/mm/internal.h
index 7e486f2c502c..10895ec52546 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -525,6 +525,8 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
atomic_set(&folio->_entire_mapcount, -1);
atomic_set(&folio->_nr_pages_mapped, 0);
atomic_set(&folio->_pincount, 0);
+ if (order > 1)
+ INIT_LIST_HEAD(&folio->_deferred_list);
}
static inline void prep_compound_tail(struct page *head, int tail_idx)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 138bcfa18234..e2334c4ee550 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7483,6 +7483,8 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug)
struct obj_cgroup *objcg;
VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
+ VM_BUG_ON_FOLIO(folio_order(folio) > 1 &&
+ !list_empty(&folio->_deferred_list), folio);
/*
* Nobody should be changing or seriously looking at
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 62240014a498..8374ba9b6249 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1006,10 +1006,11 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page)
}
break;
case 2:
- /*
- * the second tail page: ->mapping is
- * deferred_list.next -- ignore value.
- */
+ /* the second tail page: deferred_list overlaps ->mapping */
+ if (unlikely(!list_empty(&folio->_deferred_list))) {
+ bad_page(page, "on deferred list");
+ goto out;
+ }
break;
default:
if (page->mapping != TAIL_MAPPING) {
--
2.43.0
