1 files changed, 39 insertions, 16 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index a39cbed9ee17..23241c2fecce 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -34,19 +34,13 @@
  * needed for RCU lookups (because root->height is unreliable). The only
  * time callers need worry about this is when doing a lookup_slot under
  * RCU.
+ *
+ * Indirect pointer in fact is also used to tag the last pointer of a node
+ * when it is shrunk, before we rcu free the node. See shrink code for
+ * details.
  */
 #define RADIX_TREE_INDIRECT_PTR 1
-#define RADIX_TREE_RETRY ((void *)-1UL)
-
-static inline void *radix_tree_ptr_to_indirect(void *ptr)
-{
-        return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
-}
 
-static inline void *radix_tree_indirect_to_ptr(void *ptr)
-{
-        return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
-}
 #define radix_tree_indirect_to_ptr(ptr) \
         radix_tree_indirect_to_ptr((void __force *)(ptr))
 
@@ -140,16 +134,45 @@ do {									\
  *              removed.
  *
  * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
- * locked across slot lookup and dereference.  More likely, will be used with
- * radix_tree_replace_slot(), as well, so caller will hold tree write locked.
+ * locked across slot lookup and dereference. Not required if write lock is
+ * held (ie. items cannot be concurrently inserted).
+ *
+ * radix_tree_deref_retry must be used to confirm validity of the pointer if
+ * only the read lock is held.
  */
 static inline void *radix_tree_deref_slot(void **pslot)
 {
-        void *ret = rcu_dereference(*pslot);
-        if (unlikely(radix_tree_is_indirect_ptr(ret)))
-                ret = RADIX_TREE_RETRY;
-        return ret;
+        return rcu_dereference(*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
+ *
+ * radix_tree_deref_retry must be used with radix_tree_deref_slot.
+ */
+static inline int radix_tree_deref_retry(void *arg)
+{
+        return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR);
+}
+
 /**
  * radix_tree_replace_slot      - replace item in a slot
  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot