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 <[email protected]>
Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
Signed-off-by: Mike Kravetz <[email protected]>
---
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
On 2022/11/19 3:52, 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 <[email protected]>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
> Signed-off-by: Mike Kravetz <[email protected]>
Yes, PG_reserved is PF_NO_COMPOUND policy. Thanks for fixing this.
Reviewed-by: Miaohe Lin <[email protected]>
Thanks,
Miaohe Lin
Hi,
Tested it on top of v6.1.0-rc5
with 1G Hugepages on PPC64le radix MMU.
Tested-by: Tarun Sahu <[email protected]>
~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 <[email protected]>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
> Signed-off-by: Mike Kravetz <[email protected]>
> ---
> 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
>
> On Nov 19, 2022, at 03:52, Mike Kravetz <[email protected]> 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 <[email protected]>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
> Signed-off-by: Mike Kravetz <[email protected]>
Acked-by: Muchun Song <[email protected]>
Thanks.