From 471727092cd12464209b53d624430a557d402ec1 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Tue, 6 Apr 2010 22:36:20 +0100
Subject: [PATCH] --- yaml --- r: 189672 b: refs/heads/master c:
 ce82653d6cfcc95ba88c25908664878459fb1b8d h: refs/heads/master v: v3

---
 [refs]                           |  2 +-
 trunk/include/linux/radix-tree.h |  7 +++++++
 trunk/lib/radix-tree.c           | 12 ++++++------
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/[refs] b/[refs]
index ab337d7ca479..c084e10af1bb 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d3e06e2b15590b70ea73733fc4612e4741ff46e0
+refs/heads/master: ce82653d6cfcc95ba88c25908664878459fb1b8d
diff --git a/trunk/include/linux/radix-tree.h b/trunk/include/linux/radix-tree.h
index c5da74918096..55ca73cf25e5 100644
--- a/trunk/include/linux/radix-tree.h
+++ b/trunk/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/trunk/lib/radix-tree.c b/trunk/lib/radix-tree.c
index 0871582aa29d..2a087e0f9863 100644
--- a/trunk/lib/radix-tree.c
+++ b/trunk/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--;