Hi,
Tested it on top of v6.1.0-rc5
with 1G Hugepages on PPC64le radix MMU.
Tested-by: Tarun Sahu <tsahu@xxxxxxxxxxxxx>
~Tarun
On Nov 18 2022, Mike Kravetz wrote:
> 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
>
