thp: pmd_trans_huge migrate bugcheck

No pmd_trans_huge should ever materialize in migration ptes areas, because
we split the hugepage before migration ptes are instantiated.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 78adec4ba9f4..2ec5138badab 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1490,6 +1490,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
 #define FOLL_DUMP       0x08    /* give error on hole if it would be zero */
 #define FOLL_FORCE      0x10    /* get_user_pages read/write w/o permission */
 #define FOLL_MLOCK      0x40    /* mark page as mlocked */
+#define FOLL_SPLIT      0x80    /* don't return transhuge pages, split them */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
                         void *data);