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Subject[PATCH 1/2] hugetlb: fix update_and_free_page contig page struct assumption
Date
page structs are not guaranteed to be contiguous for gigantic pages.  The
routine update_and_free_page can encounter a gigantic page, yet it assumes
page structs are contiguous when setting page flags in subpages.

If update_and_free_page encounters non-contiguous page structs, we can
see “BUG: Bad page state in process …” errors.

Non-contiguous page structs are generally not an issue. However, they can
exist with a specific kernel configuration and hotplug operations. For
example: Configure the kernel with CONFIG_SPARSEMEM and
!CONFIG_SPARSEMEM_VMEMMAP. Then, hotplug add memory for the area where the
gigantic page will be allocated.
Zi Yan outlined steps to reproduce here [1].

[1] https://lore.kernel.org/linux-mm/16F7C58B-4D79-41C5-9B64-A1A1628F4AF2@nvidia.com/

Fixes: 944d9fec8d7a ("hugetlb: add support for gigantic page allocation at runtime")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: <stable@vger.kernel.org>
---
mm/hugetlb.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4bdb58ab14cb..94e9fa803294 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1312,14 +1312,16 @@ static inline void destroy_compound_gigantic_page(struct page *page,
static void update_and_free_page(struct hstate *h, struct page *page)
{
int i;
+ struct page *subpage = page;

if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
return;

h->nr_huge_pages--;
h->nr_huge_pages_node[page_to_nid(page)]--;
- for (i = 0; i < pages_per_huge_page(h); i++) {
- page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
+ for (i = 0; i < pages_per_huge_page(h);
+ i++, subpage = mem_map_next(subpage, page, i)) {
+ subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
1 << PG_referenced | 1 << PG_dirty |
1 << PG_active | 1 << PG_private |
1 << PG_writeback);
--
2.29.2
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