[PATCH] mm: thp: avoid false positive VM_BUG_ON_PAGE in page_move_anon_rmap()

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

If the page_move_anon_rmap() is refiling a pmd-splitted THP mapped in
a tail page from a pte, the "address" must be THP aligned in order for
the page->index bugcheck to pass in the CONFIG_DEBUG_VM=y builds.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: 6d0a07edd17c ("mm: thp: calculate the mapcount correctly for THP pages during WP faults")
Cc: <stable@vger.kernel.org>        [4.5]
Reported-and-Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com
---
 mm/rmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/rmap.c b/mm/rmap.c
index 8a839935b18c..0ea5d9071b32 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1098,6 +1098,8 @@ void page_move_anon_rmap(struct page *page,
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_VMA(!anon_vma, vma);
+	if (IS_ENABLED(CONFIG_DEBUG_VM) && PageTransHuge(page))
+		address &= HPAGE_PMD_MASK;
 	VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address), page);
 
 	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
-- 
2.8.1

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