1 files changed, 44 insertions, 13 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1014171dd1c5..e0ee8cb37e41 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;
                 }