lib: radix-tree: check accounting of existing slot replacement users

The bug in khugepaged fixed earlier in this series shows that radix tree slot replacement is fragile; and it will become more so when not only NULL<->!NULL transitions need to be caught but transitions from and to exceptional entries as well. We need checks. Re-implement radix_tree_replace_slot() on top of the sanity-checked __radix_tree_replace(). This requires existing callers to also pass the radix tree root, but it'll warn us when somebody replaces slots with contents that need proper accounting (transitions between NULL entries, real entries, exceptional entries) and where a replacement through the slot pointer would corrupt the radix tree node counts. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Johannes Weiner <[email protected]> Suggested-by: Jan Kara <[email protected]> Reviewed-by: Jan Kara <[email protected]> Cc: Kirill A. Shutemov <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Matthew Wilcox <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
sfionov · Dec 13, 2016 · 6d75f36 · 6d75f36
1 parent f794243
commit 6d75f36
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Showing 10 changed files with 64 additions and 40 deletions.
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
@@ -1015,7 +1015,7 @@ static inline void gmap_insert_rmap(struct gmap *sg, unsigned long vmaddr,
 	if (slot) {
 		rmap->next = radix_tree_deref_slot_protected(slot,
 							&sg->guest_table_lock);
-		radix_tree_replace_slot(slot, rmap);
+		radix_tree_replace_slot(&sg->host_to_rmap, slot, rmap);
 	} else {
 		rmap->next = NULL;
 		radix_tree_insert(&sg->host_to_rmap, vmaddr >> PAGE_SHIFT,

diff --git a/drivers/sh/intc/virq.c b/drivers/sh/intc/virq.c
@@ -254,7 +254,7 @@ static void __init intc_subgroup_map(struct intc_desc_int *d)
 
 		radix_tree_tag_clear(&d->tree, entry->enum_id,
 				     INTC_TAG_VIRQ_NEEDS_ALLOC);
-		radix_tree_replace_slot((void **)entries[i],
+		radix_tree_replace_slot(&d->tree, (void **)entries[i],
 					&intc_irq_xlate[irq]);
 	}
 

diff --git a/fs/dax.c b/fs/dax.c
@@ -342,7 +342,7 @@ static inline void *lock_slot(struct address_space *mapping, void **slot)
 		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 
 	entry |= RADIX_DAX_ENTRY_LOCK;
-	radix_tree_replace_slot(slot, (void *)entry);
+	radix_tree_replace_slot(&mapping->page_tree, slot, (void *)entry);
 	return (void *)entry;
 }
 
@@ -356,7 +356,7 @@ static inline void *unlock_slot(struct address_space *mapping, void **slot)
 		radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 
 	entry &= ~(unsigned long)RADIX_DAX_ENTRY_LOCK;
-	radix_tree_replace_slot(slot, (void *)entry);
+	radix_tree_replace_slot(&mapping->page_tree, slot, (void *)entry);
 	return (void *)entry;
 }
 

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
@@ -249,20 +249,6 @@ static inline int radix_tree_exception(void *arg)
 	return unlikely((unsigned long)arg & RADIX_TREE_ENTRY_MASK);
 }
 
-/**
- * radix_tree_replace_slot	- replace item in a slot
- * @pslot:	pointer to slot, returned by radix_tree_lookup_slot
- * @item:	new item to store in the slot.
- *
- * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
- * across slot lookup and replacement.
- */
-static inline void radix_tree_replace_slot(void **pslot, void *item)
-{
-	BUG_ON(radix_tree_is_internal_node(item));
-	rcu_assign_pointer(*pslot, item);
-}
-
 int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 			unsigned order, struct radix_tree_node **nodep,
 			void ***slotp);
@@ -280,6 +266,8 @@ void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
 void __radix_tree_replace(struct radix_tree_root *root,
 			  struct radix_tree_node *node,
 			  void **slot, void *item);
+void radix_tree_replace_slot(struct radix_tree_root *root,
+			     void **slot, void *item);
 bool __radix_tree_delete_node(struct radix_tree_root *root,
 			      struct radix_tree_node *node);
 void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
@@ -753,19 +753,10 @@ void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
 }
 EXPORT_SYMBOL(radix_tree_lookup);
 
-/**
- * __radix_tree_replace		- replace item in a slot
- * @root:	radix tree root
- * @node:	pointer to tree node
- * @slot:	pointer to slot in @node
- * @item:	new item to store in the slot.
- *
- * For use with __radix_tree_lookup().  Caller must hold tree write locked
- * across slot lookup and replacement.
- */
-void __radix_tree_replace(struct radix_tree_root *root,
-			  struct radix_tree_node *node,
-			  void **slot, void *item)
+static void replace_slot(struct radix_tree_root *root,
+			 struct radix_tree_node *node,
+			 void **slot, void *item,
+			 bool warn_typeswitch)
 {
 	void *old = rcu_dereference_raw(*slot);
 	int exceptional;
@@ -776,14 +767,58 @@ void __radix_tree_replace(struct radix_tree_root *root,
 	exceptional = !!radix_tree_exceptional_entry(item) -
 		      !!radix_tree_exceptional_entry(old);
 
-	WARN_ON_ONCE(exceptional && !node && slot != (void **)&root->rnode);
+	WARN_ON_ONCE(warn_typeswitch && exceptional);
 
 	if (node)
 		node->exceptional += exceptional;
 
 	rcu_assign_pointer(*slot, item);
 }
 
+/**
+ * __radix_tree_replace		- replace item in a slot
+ * @root:	radix tree root
+ * @node:	pointer to tree node
+ * @slot:	pointer to slot in @node
+ * @item:	new item to store in the slot.
+ *
+ * For use with __radix_tree_lookup().  Caller must hold tree write locked
+ * across slot lookup and replacement.
+ */
+void __radix_tree_replace(struct radix_tree_root *root,
+			  struct radix_tree_node *node,
+			  void **slot, void *item)
+{
+	/*
+	 * This function supports replacing exceptional entries, but
+	 * that needs accounting against the node unless the slot is
+	 * root->rnode.
+	 */
+	replace_slot(root, node, slot, item,
+		     !node && slot != (void **)&root->rnode);
+}
+
+/**
+ * radix_tree_replace_slot	- replace item in a slot
+ * @root:	radix tree root
+ * @slot:	pointer to slot
+ * @item:	new item to store in the slot.
+ *
+ * For use with radix_tree_lookup_slot(), radix_tree_gang_lookup_slot(),
+ * radix_tree_gang_lookup_tag_slot().  Caller must hold tree write locked
+ * across slot lookup and replacement.
+ *
+ * NOTE: This cannot be used to switch between non-entries (empty slots),
+ * regular entries, and exceptional entries, as that requires accounting
+ * inside the radix tree node. When switching from one type of entry to
+ * another, use __radix_tree_lookup() and __radix_tree_replace().
+ */
+void radix_tree_replace_slot(struct radix_tree_root *root,
+			     void **slot, void *item)
+{
+	replace_slot(root, NULL, slot, item, true);
+}
+
 /**
  *	radix_tree_tag_set - set a tag on a radix tree node
  *	@root:		radix tree root

diff --git a/mm/filemap.c b/mm/filemap.c
@@ -147,7 +147,7 @@ static int page_cache_tree_insert(struct address_space *mapping,
 						      false);
 		}
 	}
-	radix_tree_replace_slot(slot, page);
+	radix_tree_replace_slot(&mapping->page_tree, slot, page);
 	mapping->nrpages++;
 	if (node) {
 		workingset_node_pages_inc(node);
@@ -196,7 +196,7 @@ static void page_cache_tree_delete(struct address_space *mapping,
 			shadow = NULL;
 		}
 
-		radix_tree_replace_slot(slot, shadow);
+		radix_tree_replace_slot(&mapping->page_tree, slot, shadow);
 
 		if (!node)
 			break;

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
@@ -1426,7 +1426,7 @@ static void collapse_shmem(struct mm_struct *mm,
 		list_add_tail(&page->lru, &pagelist);
 
 		/* Finally, replace with the new page. */
-		radix_tree_replace_slot(slot,
+		radix_tree_replace_slot(&mapping->page_tree, slot,
 				new_page + (index % HPAGE_PMD_NR));
 
 		slot = radix_tree_iter_next(&iter);
@@ -1538,7 +1538,8 @@ static void collapse_shmem(struct mm_struct *mm,
 			/* Unfreeze the page. */
 			list_del(&page->lru);
 			page_ref_unfreeze(page, 2);
-			radix_tree_replace_slot(slot, page);
+			radix_tree_replace_slot(&mapping->page_tree,
+						slot, page);
 			spin_unlock_irq(&mapping->tree_lock);
 			putback_lru_page(page);
 			unlock_page(page);

diff --git a/mm/migrate.c b/mm/migrate.c
@@ -482,7 +482,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
 		SetPageDirty(newpage);
 	}
 
-	radix_tree_replace_slot(pslot, newpage);
+	radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
 
 	/*
 	 * Drop cache reference from old page by unfreezing
@@ -556,7 +556,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 
 	get_page(newpage);
 
-	radix_tree_replace_slot(pslot, newpage);
+	radix_tree_replace_slot(&mapping->page_tree, pslot, newpage);
 
 	page_ref_unfreeze(page, expected_count - 1);
 

diff --git a/mm/truncate.c b/mm/truncate.c
@@ -49,7 +49,7 @@ static void clear_exceptional_entry(struct address_space *mapping,
 		goto unlock;
 	if (*slot != entry)
 		goto unlock;
-	radix_tree_replace_slot(slot, NULL);
+	radix_tree_replace_slot(&mapping->page_tree, slot, NULL);
 	mapping->nrexceptional--;
 	if (!node)
 		goto unlock;

diff --git a/tools/testing/radix-tree/multiorder.c b/tools/testing/radix-tree/multiorder.c
@@ -146,7 +146,7 @@ static void multiorder_check(unsigned long index, int order)
 
 	slot = radix_tree_lookup_slot(&tree, index);
 	free(*slot);
-	radix_tree_replace_slot(slot, item2);
+	radix_tree_replace_slot(&tree, slot, item2);
 	for (i = min; i < max; i++) {
 		struct item *item = item_lookup(&tree, i);
 		assert(item != 0);