1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index ab2baa5c4884..23241c2fecce 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -146,6 +146,22 @@ static inline void *radix_tree_deref_slot(void **pslot)
 }
 
 /**
+ * radix_tree_deref_slot_protected      - dereference a slot without RCU lock but with tree lock held
+ * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
+ * Returns:     item that was stored in that slot with any direct pointer flag
+ *              removed.
+ *
+ * Similar to radix_tree_deref_slot but only used during migration when a pages
+ * mapping is being moved. The caller does not hold the RCU read lock but it
+ * must hold the tree lock to prevent parallel updates.
+ */
+static inline void *radix_tree_deref_slot_protected(void **pslot,
+                                                        spinlock_t *treelock)
+{
+        return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
+}
+
+/**
  * radix_tree_deref_retry       - check radix_tree_deref_slot
  * @arg:        pointer returned by radix_tree_deref_slot
  * Returns:     0 if retry is not required, otherwise retry is required