mm/hugetlb: use nth_page() in place of direct struct page manipulation

[ Upstream commit 426056efe835cf4864ccf4c328fe3af9146fc539 ]

When dealing with hugetlb pages, manipulating struct page pointers
directly can get to wrong struct page, since struct page is not guaranteed
to be contiguous on SPARSEMEM without VMEMMAP.  Use nth_page() to handle
it properly.

A wrong or non-existing page might be tried to be grabbed, either
leading to a non freeable page or kernel memory access errors.  No bug
is reported.  It comes from code inspection.

Link: https://lkml.kernel.org/r/20230913201248.452081-3-zi.yan@sent.com


Fixes: 57a196a5 ("hugetlb: simplify hugetlb handling in follow_page_mask")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>