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...
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);