From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
---
diff --git a/mm/rmap.c b/mm/rmap.c
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -815,6 +815,7 @@ static void __page_check_anon_rmap(struc
* 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
}
@@ -1405,6 +1406,7 @@ 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);
@@ -1416,6 +1418,7 @@ void drop_anon_vma(struct anon_vma *anon
* 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);
}
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