Commit 2b21624fc232 ("hugetlb: freeze allocated pages before creating
hugetlb pages") changed the order page flags were cleared and set in the
head page. It moved the __ClearPageReserved after __SetPageHead.
However, there is a check to make sure __ClearPageReserved is never
done on a head page. If CONFIG_DEBUG_VM_PGFLAGS is enabled, the
following BUG will be hit when creating a hugetlb gigantic page:
page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
------------[ cut here ]------------
kernel BUG at include/linux/page-flags.h:500!
Call Trace will differ depending on whether hugetlb page is created
at boot time or run time.
Make sure to __ClearPageReserved BEFORE __SetPageHead.
Reported-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/hugetlb.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e48f8ef45b17..f1385c3b6c96 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1800,6 +1800,7 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order,
/* we rely on prep_new_huge_page to set the destructor */
set_compound_order(page, order);
+ __ClearPageReserved(page);
__SetPageHead(page);
for (i = 0; i < nr_pages; i++) {
p = nth_page(page, i);
@@ -1816,7 +1817,8 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order,
* on the head page when they need know if put_page() is needed
* after get_user_pages().
*/
- __ClearPageReserved(p);
+ if (i != 0) /* head page cleared above */
+ __ClearPageReserved(p);
/*
* Subtle and very unlikely
*
--
2.38.1
