rmap: add anon_vma bug checks
Andrea Arcangeli [Tue, 10 Aug 2010 00:19:10 +0000 (17:19 -0700)]
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>

mm/rmap.c

index 2f855ba..4d152a6 100644 (file)
--- 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);
                }