1 files changed, 25 insertions, 9 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 87b9e8ad4509..9d2ba01bd4f9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -316,7 +316,7 @@ void __init anon_vma_init(void)
  */
 struct anon_vma *page_lock_anon_vma(struct page *page)
 {
-        struct anon_vma *anon_vma;
+        struct anon_vma *anon_vma, *root_anon_vma;
         unsigned long anon_mapping;
 
         rcu_read_lock();
@@ -327,8 +327,21 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
                 goto out;
 
         anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
-        anon_vma_lock(anon_vma);
-        return anon_vma;
+        root_anon_vma = ACCESS_ONCE(anon_vma->root);
+        spin_lock(&root_anon_vma->lock);
+
+        /*
+         * If this page is still mapped, then its anon_vma cannot have been
+         * freed.  But if it has been unmapped, we have no security against
+         * the anon_vma structure being freed and reused (for another anon_vma:
+         * SLAB_DESTROY_BY_RCU guarantees that - so the spin_lock above cannot
+         * corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting
+         * anon_vma->root before page_unlock_anon_vma() is called to unlock.
+         */
+        if (page_mapped(page))
+                return anon_vma;
+
+        spin_unlock(&root_anon_vma->lock);
 out:
         rcu_read_unlock();
         return NULL;
@@ -1551,13 +1564,14 @@ static void __hugepage_set_anon_rmap(struct page *page,
         struct vm_area_struct *vma, unsigned long address, int exclusive)
 {
         struct anon_vma *anon_vma = vma->anon_vma;
+
         BUG_ON(!anon_vma);
-        if (!exclusive) {
-                struct anon_vma_chain *avc;
-                avc = list_entry(vma->anon_vma_chain.prev,
-                                 struct anon_vma_chain, same_vma);
-                anon_vma = avc->anon_vma;
-        }
+
+        if (PageAnon(page))
+                return;
+        if (!exclusive)
+                anon_vma = anon_vma->root;
+
         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
         page->mapping = (struct address_space *) anon_vma;
         page->index = linear_page_index(vma, address);
@@ -1568,6 +1582,8 @@ void hugepage_add_anon_rmap(struct page *page,
 {
         struct anon_vma *anon_vma = vma->anon_vma;
         int first;
+
+        BUG_ON(!PageLocked(page));
         BUG_ON(!anon_vma);
         BUG_ON(address < vma->vm_start || address >= vma->vm_end);
         first = atomic_inc_and_test(&page->_mapcount);