For compound pages, the head sets the PG_head flag and
the tail sets the compound_head to indicate the head page.
If a user allocates a compound page and frees it with a different
order, the compound page information will not be properly
initialized. To detect this problem, compound_page(page) and
the order are compared, but it is not checked when the order is 0.
That error should be checked regardless of the order.
Signed-off-by: Hyesoo Yu <[email protected]>
---
mm/page_alloc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 95546f376302..fc92ac93c7c8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1078,6 +1078,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
int bad = 0;
bool skip_kasan_poison = should_skip_kasan_poison(page, fpi_flags);
bool init = want_init_on_free();
+ bool compound = PageCompound(page);
VM_BUG_ON_PAGE(PageTail(page), page);
@@ -1096,16 +1097,15 @@ static __always_inline bool free_pages_prepare(struct page *page,
return false;
}
+ VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
+
/*
* Check tail pages before head page information is cleared to
* avoid checking PageCompound for order-0 pages.
*/
if (unlikely(order)) {
- bool compound = PageCompound(page);
int i;
- VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
-
if (compound)
page[1].flags &= ~PAGE_FLAGS_SECOND;
for (i = 1; i < (1 << order); i++) {
--
2.25.1
On Thu, Oct 12, 2023 at 10:11:06AM +0900, Hyesoo Yu wrote:
> For compound pages, the head sets the PG_head flag and
> the tail sets the compound_head to indicate the head page.
> If a user allocates a compound page and frees it with a different
> order, the compound page information will not be properly
> initialized. To detect this problem, compound_page(page) and
> the order are compared, but it is not checked when the order is 0.
> That error should be checked regardless of the order.
I believe all compound pages are order >= 1, so this error can't occur
when the order is 0.