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-rw-r--r--include/linux/radix-tree.h7
-rw-r--r--lib/radix-tree.c12
2 files changed, 13 insertions, 6 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index c5da74918096..55ca73cf25e5 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 0871582aa29d..2a087e0f9863 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--;