2 files changed, 13 insertions, 6 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index c5da7491809..55ca73cf25e 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -121,6 +121,13 @@ do {									\
  * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
  * access to data items when inserting into or looking up from the radix tree)
  *
+ * Note that the value returned by radix_tree_tag_get() may not be relied upon
+ * if only the RCU read lock is held.  Functions to set/clear tags and to
+ * delete nodes running concurrently with it may affect its result such that
+ * two consecutive reads in the same locked section may return different
+ * values.  If reliability is required, modification functions must also be
+ * excluded from concurrency.
+ *
  * radix_tree_tagged is able to be called without locking or RCU.
  */
 
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 0871582aa29..2a087e0f986 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -555,6 +555,10 @@ EXPORT_SYMBOL(radix_tree_tag_clear);
  *
  *  0: tag not present or not set
  *  1: tag set
+ *
+ * Note that the return value of this function may not be relied on, even if
+ * the RCU lock is held, unless tag modification and node deletion are excluded
+ * from concurrency.
  */
 int radix_tree_tag_get(struct radix_tree_root *root,
                         unsigned long index, unsigned int tag)
@@ -595,12 +599,8 @@ int radix_tree_tag_get(struct radix_tree_root *root,
                  */
                 if (!tag_get(node, tag, offset))
                         saw_unset_tag = 1;
-                if (height == 1) {
-                        int ret = tag_get(node, tag, offset);
-
-                        BUG_ON(ret && saw_unset_tag);
-                        return !!ret;
-                }
+                if (height == 1)
+                        return !!tag_get(node, tag, offset);
                 node = rcu_dereference_raw(node->slots[offset]);
                 shift -= RADIX_TREE_MAP_SHIFT;
                 height--;