1 files changed, 151 insertions, 44 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 8da044a..0eb463e 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -24,8 +24,8 @@
  *   inode->i_alloc_sem (vmtruncate_range)
  *   mm->mmap_sem
  *     page->flags PG_locked (lock_page)
- *       mapping->i_mmap_lock
- *         anon_vma->lock
+ *       mapping->i_mmap_mutex
+ *         anon_vma->mutex
  *           mm->page_table_lock or pte_lock
  *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
  *             swap_lock (in swap_duplicate, swap_info_get)
@@ -40,7 +40,7 @@
  *
  * (code doesn't rely on that order so it could be switched around)
  * ->tasklist_lock
- *   anon_vma->lock      (memory_failure, collect_procs_anon)
+ *   anon_vma->mutex      (memory_failure, collect_procs_anon)
  *     pte map lock
  */
 
@@ -86,6 +86,29 @@ static inline struct anon_vma *anon_vma_alloc(void)
 static inline void anon_vma_free(struct anon_vma *anon_vma)
 {
 	VM_BUG_ON(atomic_read(&anon_vma->refcount));
+
+	/*
+	 * Synchronize against page_lock_anon_vma() such that
+	 * we can safely hold the lock without the anon_vma getting
+	 * freed.
+	 *
+	 * Relies on the full mb implied by the atomic_dec_and_test() from
+	 * put_anon_vma() against the acquire barrier implied by
+	 * mutex_trylock() from page_lock_anon_vma(). This orders:
+	 *
+	 * page_lock_anon_vma()		VS	put_anon_vma()
+	 *   mutex_trylock()			  atomic_dec_and_test()
+	 *   LOCK				  MB
+	 *   atomic_read()			  mutex_is_locked()
+	 *
+	 * LOCK should suffice since the actual taking of the lock must
+	 * happen _before_ what follows.
+	 */
+	if (mutex_is_locked(&anon_vma->root->mutex)) {
+		anon_vma_lock(anon_vma);
+		anon_vma_unlock(anon_vma);
+	}
+
 	kmem_cache_free(anon_vma_cachep, anon_vma);
 }
 
@@ -307,7 +330,7 @@ static void anon_vma_ctor(void *data)
 {
 	struct anon_vma *anon_vma = data;
 
-	spin_lock_init(&anon_vma->lock);
+	mutex_init(&anon_vma->mutex);
 	atomic_set(&anon_vma->refcount, 0);
 	INIT_LIST_HEAD(&anon_vma->head);
 }
@@ -320,12 +343,31 @@ void __init anon_vma_init(void)
 }
 
 /*
- * Getting a lock on a stable anon_vma from a page off the LRU is
- * tricky: page_lock_anon_vma rely on RCU to guard against the races.
+ * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
+ *
+ * Since there is no serialization what so ever against page_remove_rmap()
+ * the best this function can do is return a locked anon_vma that might
+ * have been relevant to this page.
+ *
+ * The page might have been remapped to a different anon_vma or the anon_vma
+ * returned may already be freed (and even reused).
+ *
+ * In case it was remapped to a different anon_vma, the new anon_vma will be a
+ * child of the old anon_vma, and the anon_vma lifetime rules will therefore
+ * ensure that any anon_vma obtained from the page will still be valid for as
+ * long as we observe page_mapped() [ hence all those page_mapped() tests ].
+ *
+ * All users of this function must be very careful when walking the anon_vma
+ * chain and verify that the page in question is indeed mapped in it
+ * [ something equivalent to page_mapped_in_vma() ].
+ *
+ * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
+ * that the anon_vma pointer from page->mapping is valid if there is a
+ * mapcount, we can dereference the anon_vma after observing those.
  */
-struct anon_vma *__page_lock_anon_vma(struct page *page)
+struct anon_vma *page_get_anon_vma(struct page *page)
 {
-	struct anon_vma *anon_vma, *root_anon_vma;
+	struct anon_vma *anon_vma = NULL;
 	unsigned long anon_mapping;
 
 	rcu_read_lock();
@@ -336,32 +378,100 @@ struct anon_vma *__page_lock_anon_vma(struct page *page)
 		goto out;
 
 	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
-	root_anon_vma = ACCESS_ONCE(anon_vma->root);
-	spin_lock(&root_anon_vma->lock);
+	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
+		anon_vma = NULL;
+		goto out;
+	}
 
 	/*
 	 * 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.
+	 * 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 atomic_inc_not_zero()
+	 * above cannot corrupt).
 	 */
-	if (page_mapped(page))
-		return anon_vma;
+	if (!page_mapped(page)) {
+		put_anon_vma(anon_vma);
+		anon_vma = NULL;
+	}
+out:
+	rcu_read_unlock();
+
+	return anon_vma;
+}
+
+/*
+ * Similar to page_get_anon_vma() except it locks the anon_vma.
+ *
+ * Its a little more complex as it tries to keep the fast path to a single
+ * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
+ * reference like with page_get_anon_vma() and then block on the mutex.
+ */
+struct anon_vma *page_lock_anon_vma(struct page *page)
+{
+	struct anon_vma *anon_vma = NULL;
+	struct anon_vma *root_anon_vma;
+	unsigned long anon_mapping;
+
+	rcu_read_lock();
+	anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
+	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
+		goto out;
+	if (!page_mapped(page))
+		goto out;
+
+	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
+	root_anon_vma = ACCESS_ONCE(anon_vma->root);
+	if (mutex_trylock(&root_anon_vma->mutex)) {
+		/*
+		 * If the page is still mapped, then this anon_vma is still
+		 * its anon_vma, and holding the mutex ensures that it will
+		 * not go away, see anon_vma_free().
+		 */
+		if (!page_mapped(page)) {
+			mutex_unlock(&root_anon_vma->mutex);
+			anon_vma = NULL;
+		}
+		goto out;
+	}
+
+	/* trylock failed, we got to sleep */
+	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
+		anon_vma = NULL;
+		goto out;
+	}
+
+	if (!page_mapped(page)) {
+		put_anon_vma(anon_vma);
+		anon_vma = NULL;
+		goto out;
+	}
+
+	/* we pinned the anon_vma, its safe to sleep */
+	rcu_read_unlock();
+	anon_vma_lock(anon_vma);
+
+	if (atomic_dec_and_test(&anon_vma->refcount)) {
+		/*
+		 * Oops, we held the last refcount, release the lock
+		 * and bail -- can't simply use put_anon_vma() because
+		 * we'll deadlock on the anon_vma_lock() recursion.
+		 */
+		anon_vma_unlock(anon_vma);
+		__put_anon_vma(anon_vma);
+		anon_vma = NULL;
+	}
+
+	return anon_vma;
 
-	spin_unlock(&root_anon_vma->lock);
 out:
 	rcu_read_unlock();
-	return NULL;
+	return anon_vma;
 }
 
 void page_unlock_anon_vma(struct anon_vma *anon_vma)
-	__releases(&anon_vma->root->lock)
-	__releases(RCU)
 {
 	anon_vma_unlock(anon_vma);
-	rcu_read_unlock();
 }
 
 /*
@@ -646,14 +756,14 @@ static int page_referenced_file(struct page *page,
 	 * The page lock not only makes sure that page->mapping cannot
 	 * suddenly be NULLified by truncation, it makes sure that the
 	 * structure at mapping cannot be freed and reused yet,
-	 * so we can safely take mapping->i_mmap_lock.
+	 * so we can safely take mapping->i_mmap_mutex.
 	 */
 	BUG_ON(!PageLocked(page));
 
-	spin_lock(&mapping->i_mmap_lock);
+	mutex_lock(&mapping->i_mmap_mutex);
 
 	/*
-	 * i_mmap_lock does not stabilize mapcount at all, but mapcount
+	 * i_mmap_mutex does not stabilize mapcount at all, but mapcount
 	 * is more likely to be accurate if we note it after spinning.
 	 */
 	mapcount = page_mapcount(page);
@@ -675,7 +785,7 @@ static int page_referenced_file(struct page *page,
 			break;
 	}
 
-	spin_unlock(&mapping->i_mmap_lock);
+	mutex_unlock(&mapping->i_mmap_mutex);
 	return referenced;
 }
 
@@ -719,7 +829,7 @@ int page_referenced(struct page *page,
 			unlock_page(page);
 	}
 out:
-	if (page_test_and_clear_young(page))
+	if (page_test_and_clear_young(page_to_pfn(page)))
 		referenced++;
 
 	return referenced;
@@ -762,7 +872,7 @@ static int page_mkclean_file(struct address_space *mapping, struct page *page)
 
 	BUG_ON(PageAnon(page));
 
-	spin_lock(&mapping->i_mmap_lock);
+	mutex_lock(&mapping->i_mmap_mutex);
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
 		if (vma->vm_flags & VM_SHARED) {
 			unsigned long address = vma_address(page, vma);
@@ -771,7 +881,7 @@ static int page_mkclean_file(struct address_space *mapping, struct page *page)
 			ret += page_mkclean_one(page, vma, address);
 		}
 	}
-	spin_unlock(&mapping->i_mmap_lock);
+	mutex_unlock(&mapping->i_mmap_mutex);
 	return ret;
 }
 
@@ -785,10 +895,8 @@ int page_mkclean(struct page *page)
 		struct address_space *mapping = page_mapping(page);
 		if (mapping) {
 			ret = page_mkclean_file(mapping, page);
-			if (page_test_dirty(page)) {
-				page_clear_dirty(page, 1);
+			if (page_test_and_clear_dirty(page_to_pfn(page), 1))
 				ret = 1;
-			}
 		}
 	}
 
@@ -914,7 +1022,7 @@ void do_page_add_anon_rmap(struct page *page,
 		return;
 
 	VM_BUG_ON(!PageLocked(page));
-	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
+	/* address might be in next vma when migration races vma_adjust */
 	if (first)
 		__page_set_anon_rmap(page, vma, address, exclusive);
 	else
@@ -981,10 +1089,9 @@ void page_remove_rmap(struct page *page)
 	 * not if it's in swapcache - there might be another pte slot
 	 * containing the swap entry, but page not yet written to swap.
 	 */
-	if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) {
-		page_clear_dirty(page, 1);
+	if ((!PageAnon(page) || PageSwapCache(page)) &&
+	    page_test_and_clear_dirty(page_to_pfn(page), 1))
 		set_page_dirty(page);
-	}
 	/*
 	 * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
 	 * and not charged by memcg for now.
@@ -1122,7 +1229,7 @@ out_mlock:
 	/*
 	 * We need mmap_sem locking, Otherwise VM_LOCKED check makes
 	 * unstable result and race. Plus, We can't wait here because
-	 * we now hold anon_vma->lock or mapping->i_mmap_lock.
+	 * we now hold anon_vma->mutex or mapping->i_mmap_mutex.
 	 * if trylock failed, the page remain in evictable lru and later
 	 * vmscan could retry to move the page to unevictable lru if the
 	 * page is actually mlocked.
@@ -1348,7 +1455,7 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 	unsigned long max_nl_size = 0;
 	unsigned int mapcount;
 
-	spin_lock(&mapping->i_mmap_lock);
+	mutex_lock(&mapping->i_mmap_mutex);
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
 		if (address == -EFAULT)
@@ -1394,7 +1501,7 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 	mapcount = page_mapcount(page);
 	if (!mapcount)
 		goto out;
-	cond_resched_lock(&mapping->i_mmap_lock);
+	cond_resched();
 
 	max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
 	if (max_nl_cursor == 0)
@@ -1416,7 +1523,7 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 			}
 			vma->vm_private_data = (void *) max_nl_cursor;
 		}
-		cond_resched_lock(&mapping->i_mmap_lock);
+		cond_resched();
 		max_nl_cursor += CLUSTER_SIZE;
 	} while (max_nl_cursor <= max_nl_size);
 
@@ -1428,7 +1535,7 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
 		vma->vm_private_data = NULL;
 out:
-	spin_unlock(&mapping->i_mmap_lock);
+	mutex_unlock(&mapping->i_mmap_mutex);
 	return ret;
 }
 
@@ -1547,7 +1654,7 @@ static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
 
 	if (!mapping)
 		return ret;
-	spin_lock(&mapping->i_mmap_lock);
+	mutex_lock(&mapping->i_mmap_mutex);
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
 		if (address == -EFAULT)
@@ -1561,7 +1668,7 @@ static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
 	 * never contain migration ptes.  Decide what to do about this
 	 * limitation to linear when we need rmap_walk() on nonlinear.
 	 */
-	spin_unlock(&mapping->i_mmap_lock);
+	mutex_unlock(&mapping->i_mmap_mutex);
 	return ret;
 }
 
@@ -1610,7 +1717,7 @@ void hugepage_add_anon_rmap(struct page *page,
 
 	BUG_ON(!PageLocked(page));
 	BUG_ON(!anon_vma);
-	BUG_ON(address < vma->vm_start || address >= vma->vm_end);
+	/* address might be in next vma when migration races vma_adjust */
 	first = atomic_inc_and_test(&page->_mapcount);
 	if (first)
 		__hugepage_set_anon_rmap(page, vma, address, 0);