mm/memory_hotplug: use pfn math in place of direct struct page manipulation

commit 1640a0ef80f6d572725f5b0330038c18e98ea168 upstream.

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 pfn calculation to
handle it properly.

Without the fix, a wrong number of page might be skipped. Since skip cannot be
negative, scan_movable_page() will end early and might miss a movable page with
-ENOENT. This might fail offline_pages(). No bug is reported. The fix comes
from code inspection.

Link: https://lkml.kernel.org/r/20230913201248.452081-4-zi.yan@sent.com
Fixes: eeb0efd071d8 ("mm,memory_hotplug: fix scan_movable_pages() for gigantic hugepages")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 81f2a97c886c9e5fb8323b62d9c6046a391fbe92..bf611c55fc66bf1c73b0a436ca11f9823ed09dc4 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1677,7 +1677,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
                 */
                if (HPageMigratable(head))
                        goto found;
-               skip = compound_nr(head) - (page - head);
+               skip = compound_nr(head) - (pfn - page_to_pfn(head));
                pfn += skip - 1;
        }
        return -ENOENT;