1 files changed, 44 insertions, 13 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1014171..e0ee8cb 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -625,6 +625,13 @@ EXPORT_SYMBOL(radix_tree_tag_get);
  * also settag. The function stops either after tagging nr_to_tag items or
  * after reaching last_index.
  *
+ * The tags must be set from the leaf level only and propagated back up the
+ * path to the root. We must do this so that we resolve the full path before
+ * setting any tags on intermediate nodes. If we set tags as we descend, then
+ * we can get to the leaf node and find that the index that has the iftag
+ * set is outside the range we are scanning. This reults in dangling tags and
+ * can lead to problems with later tag operations (e.g. livelocks on lookups).
+ *
  * The function returns number of leaves where the tag was set and sets
  * *first_indexp to the first unscanned index.
  */
@@ -633,9 +640,13 @@ unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 		unsigned long nr_to_tag,
 		unsigned int iftag, unsigned int settag)
 {
-	unsigned int height = root->height, shift;
-	unsigned long tagged = 0, index = *first_indexp;
-	struct radix_tree_node *open_slots[height], *slot;
+	unsigned int height = root->height;
+	struct radix_tree_path path[height];
+	struct radix_tree_path *pathp = path;
+	struct radix_tree_node *slot;
+	unsigned int shift;
+	unsigned long tagged = 0;
+	unsigned long index = *first_indexp;
 
 	last_index = min(last_index, radix_tree_maxindex(height));
 	if (index > last_index)
@@ -655,6 +666,13 @@ unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 	slot = radix_tree_indirect_to_ptr(root->rnode);
 
+	/*
+	 * we fill the path from (root->height - 2) to 0, leaving the index at
+	 * (root->height - 1) as a terminator. Zero the node in the terminator
+	 * so that we can use this to end walk loops back up the path.
+	 */
+	path[height - 1].node = NULL;
+
 	for (;;) {
 		int offset;
 
@@ -663,17 +681,30 @@ unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 			goto next;
 		if (!tag_get(slot, iftag, offset))
 			goto next;
+		if (height > 1) {
+			/* Go down one level */
+			height--;
+			shift -= RADIX_TREE_MAP_SHIFT;
+			path[height - 1].node = slot;
+			path[height - 1].offset = offset;
+			slot = slot->slots[offset];
+			continue;
+		}
+
+		/* tag the leaf */
+		tagged++;
 		tag_set(slot, settag, offset);
-		if (height == 1) {
-			tagged++;
-			goto next;
+
+		/* walk back up the path tagging interior nodes */
+		pathp = &path[0];
+		while (pathp->node) {
+			/* stop if we find a node with the tag already set */
+			if (tag_get(pathp->node, settag, pathp->offset))
+				break;
+			tag_set(pathp->node, settag, pathp->offset);
+			pathp++;
 		}
-		/* Go down one level */
-		height--;
-		shift -= RADIX_TREE_MAP_SHIFT;
-		open_slots[height] = slot;
-		slot = slot->slots[offset];
-		continue;
+
 next:
 		/* Go to next item at level determined by 'shift' */
 		index = ((index >> shift) + 1) << shift;
@@ -687,7 +718,7 @@ next:
 			 * last_index is guaranteed to be in the tree, what
 			 * we do below cannot wander astray.
 			 */
-			slot = open_slots[height];
+			slot = path[height - 1].node;
 			height++;
 			shift += RADIX_TREE_MAP_SHIFT;
 		}