diff options
| -rw-r--r-- | mm/rmap.c | 19 |
1 files changed, 16 insertions, 3 deletions
@@ -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; |
