rmap: add anon_vma bug checks

Verify the refcounting doesn't go wrong, and resurrect the check in
__page_check_anon_rmap as in old anon-vma code.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-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, 3 insertions, 0 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 2f855babfd06..4d152a6d3a89 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -811,6 +811,7 @@ static void __page_check_anon_rmap(struct page *page,
          * are initially only visible via the pagetables, and the pte is locked
          * over the call to page_add_new_anon_rmap.
          */
+        BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
         BUG_ON(page->index != linear_page_index(vma, address));
 #endif
 }
@@ -1408,6 +1409,7 @@ int try_to_munlock(struct page *page)
  */
 void drop_anon_vma(struct anon_vma *anon_vma)
 {
+        BUG_ON(atomic_read(&anon_vma->external_refcount) <= 0);
         if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
                 struct anon_vma *root = anon_vma->root;
                 int empty = list_empty(&anon_vma->head);
@@ -1419,6 +1421,7 @@ void drop_anon_vma(struct anon_vma *anon_vma)
                  * the refcount on the root and check if we need to free it.
                  */
                 if (empty && anon_vma != root) {
+                        BUG_ON(atomic_read(&root->external_refcount) <= 0);
                         last_root_user = atomic_dec_and_test(&root->external_refcount);
                         root_empty = list_empty(&root->head);
                 }