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>

3 files changed, 12 insertions, 1 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);
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;
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 690d0de993af..1a531b760b3b 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -113,6 +113,8 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
                         goto out;
 
                 pmd = pmd_offset(pud, addr);
+                if (pmd_trans_huge(*pmd))
+                        goto out;
                 if (!pmd_present(*pmd))
                         goto out;
 
@@ -632,6 +634,9 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
                 /* page was freed from under us. So we are done. */
                 goto move_newpage;
         }
+        if (unlikely(PageTransHuge(page)))
+                if (unlikely(split_huge_page(page)))
+                        goto move_newpage;
 
         /* prepare cgroup just returns 0 or -ENOMEM */
         rc = -EAGAIN;
@@ -1063,7 +1068,7 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
                 if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
                         goto set_status;
 
-                page = follow_page(vma, pp->addr, FOLL_GET);
+                page = follow_page(vma, pp->addr, FOLL_GET|FOLL_SPLIT);
 
                 err = PTR_ERR(page);
                 if (IS_ERR(page))