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, 5 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index c1a80e00458d..12ee1ea237f5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1305,6 +1305,10 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                 goto out;
         }
         if (pmd_trans_huge(*pmd)) {
+                if (flags & FOLL_SPLIT) {
+                        split_huge_page_pmd(mm, pmd);
+                        goto split_fallthrough;
+                }
                 spin_lock(&mm->page_table_lock);
                 if (likely(pmd_trans_huge(*pmd))) {
                         if (unlikely(pmd_trans_splitting(*pmd))) {
@@ -1320,6 +1324,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                         spin_unlock(&mm->page_table_lock);
                 /* fall through */
         }
+split_fallthrough:
         if (unlikely(pmd_bad(*pmd)))
                 goto no_page_table;