radix-tree: improve multiorder iterators

This fixes several interlinked problems with the iterators in the
presence of multiorder entries.

1. radix_tree_iter_next() would only advance by one slot, which would
   result in the iterators returning the same entry more than once if
   there were sibling entries.

2. radix_tree_next_slot() could return an internal pointer instead of
   a user pointer if a tagged multiorder entry was immediately followed by
   an entry of lower order.

3. radix_tree_next_slot() expanded to a lot more code than it used to
   when multiorder support was compiled in.  And I wasn't comfortable with
   entry_to_node() being in a header file.

Fixing radix_tree_iter_next() for the presence of sibling entries
necessarily involves examining the contents of the radix tree, so we now
need to pass 'slot' to radix_tree_iter_next(), and we need to change the
calling convention so it is called *before* dropping the lock which
protects the tree.  Also rename it to radix_tree_iter_resume(), as some
people thought it was necessary to call radix_tree_iter_next() each time
around the loop.

radix_tree_next_slot() becomes closer to how it looked before multiorder
support was introduced.  It only checks to see if the next entry in the
chunk is a sibling entry or a pointer to a node; this should be rare
enough that handling this case out of line is not a performance impact
(and such impact is amortised by the fact that the entry we just
processed was a multiorder entry).  Also, radix_tree_next_slot() used to
force a new chunk lookup for untagged entries, which is more expensive
than the out of line sibling entry skipping.

Link: http://lkml.kernel.org/r/1480369871-5271-55-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

9 files changed, 188 insertions, 85 deletions

diff --git a/fs/btrfs/tests/btrfs-tests.c b/fs/btrfs/tests/btrfs-tests.c
index 73076a0ea6a9..00ee006a8aa2 100644
--- a/fs/btrfs/tests/btrfs-tests.c
+++ b/fs/btrfs/tests/btrfs-tests.c
@@ -162,7 +162,7 @@ void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
                                 slot = radix_tree_iter_retry(&iter);
                         continue;
                 }
-                slot = radix_tree_iter_next(&iter);
+                slot = radix_tree_iter_resume(slot, &iter);
                 spin_unlock(&fs_info->buffer_lock);
                 free_extent_buffer_stale(eb);
                 spin_lock(&fs_info->buffer_lock);
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index d04073ac3a9f..289d007d487b 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -403,20 +403,17 @@ __radix_tree_iter_add(struct radix_tree_iter *iter, unsigned long slots)
 }
 
 /**
- * radix_tree_iter_next - resume iterating when the chunk may be invalid
- * @iter:       iterator state
+ * radix_tree_iter_resume - resume iterating when the chunk may be invalid
+ * @slot: pointer to current slot
+ * @iter: iterator state
+ * Returns: New slot pointer
  *
  * If the iterator needs to release then reacquire a lock, the chunk may
  * have been invalidated by an insertion or deletion.  Call this function
- * to continue the iteration from the next index.
+ * before releasing the lock to continue the iteration from the next index.
  */
-static inline __must_check
-void **radix_tree_iter_next(struct radix_tree_iter *iter)
-{
-        iter->next_index = __radix_tree_iter_add(iter, 1);
-        iter->tags = 0;
-        return NULL;
-}
+void **__must_check radix_tree_iter_resume(void **slot,
+                                        struct radix_tree_iter *iter);
 
 /**
  * radix_tree_chunk_size - get current chunk size
@@ -430,10 +427,17 @@ radix_tree_chunk_size(struct radix_tree_iter *iter)
         return (iter->next_index - iter->index) >> iter_shift(iter);
 }
 
-static inline struct radix_tree_node *entry_to_node(void *ptr)
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+void ** __radix_tree_next_slot(void **slot, struct radix_tree_iter *iter,
+                                unsigned flags);
+#else
+/* Can't happen without sibling entries, but the compiler can't tell that */
+static inline void ** __radix_tree_next_slot(void **slot,
+                                struct radix_tree_iter *iter, unsigned flags)
 {
-        return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
+        return slot;
 }
+#endif
 
 /**
  * radix_tree_next_slot - find next slot in chunk
@@ -447,7 +451,7 @@ static inline struct radix_tree_node *entry_to_node(void *ptr)
  * For tagged lookup it also eats @iter->tags.
  *
  * There are several cases where 'slot' can be passed in as NULL to this
- * function.  These cases result from the use of radix_tree_iter_next() or
+ * function.  These cases result from the use of radix_tree_iter_resume() or
  * radix_tree_iter_retry().  In these cases we don't end up dereferencing
  * 'slot' because either:
  * a) we are doing tagged iteration and iter->tags has been set to 0, or
@@ -458,51 +462,31 @@ static __always_inline void **
 radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
 {
         if (flags & RADIX_TREE_ITER_TAGGED) {
-                void *canon = slot;
-
                 iter->tags >>= 1;
                 if (unlikely(!iter->tags))
                         return NULL;
-                while (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
-                                        radix_tree_is_internal_node(slot[1])) {
-                        if (entry_to_node(slot[1]) == canon) {
-                                iter->tags >>= 1;
-                                iter->index = __radix_tree_iter_add(iter, 1);
-                                slot++;
-                                continue;
-                        }
-                        iter->next_index = __radix_tree_iter_add(iter, 1);
-                        return NULL;
-                }
                 if (likely(iter->tags & 1ul)) {
                         iter->index = __radix_tree_iter_add(iter, 1);
-                        return slot + 1;
+                        slot++;
+                        goto found;
                 }
                 if (!(flags & RADIX_TREE_ITER_CONTIG)) {
                         unsigned offset = __ffs(iter->tags);
 
-                        iter->tags >>= offset;
-                        iter->index = __radix_tree_iter_add(iter, offset + 1);
-                        return slot + offset + 1;
+                        iter->tags >>= offset++;
+                        iter->index = __radix_tree_iter_add(iter, offset);
+                        slot += offset;
+                        goto found;
                 }
         } else {
                 long count = radix_tree_chunk_size(iter);
-                void *canon = slot;
 
                 while (--count > 0) {
                         slot++;
                         iter->index = __radix_tree_iter_add(iter, 1);
 
-                        if (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
-                            radix_tree_is_internal_node(*slot)) {
-                                if (entry_to_node(*slot) == canon)
-                                        continue;
-                                iter->next_index = iter->index;
-                                break;
-                        }
-
                         if (likely(*slot))
-                                return slot;
+                                goto found;
                         if (flags & RADIX_TREE_ITER_CONTIG) {
                                 /* forbid switching to the next chunk */
                                 iter->next_index = 0;
@@ -511,6 +495,11 @@ radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
                 }
         }
         return NULL;
+
+ found:
+        if (unlikely(radix_tree_is_internal_node(*slot)))
+                return __radix_tree_next_slot(slot, iter, flags);
+        return slot;
 }
 
 /**
@@ -561,6 +550,6 @@ radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
              slot || (slot = radix_tree_next_chunk(root, iter,          \
                               RADIX_TREE_ITER_TAGGED | tag)) ;          \
              slot = radix_tree_next_slot(slot, iter,                    \
-                                RADIX_TREE_ITER_TAGGED))
+                                RADIX_TREE_ITER_TAGGED | tag))
 
 #endif /* _LINUX_RADIX_TREE_H */
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index dbf4e8c8e100..0a7ac0fb4a65 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -69,6 +69,11 @@ struct radix_tree_preload {
 };
 static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
 
+static inline struct radix_tree_node *entry_to_node(void *ptr)
+{
+        return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
+}
+
 static inline void *node_to_entry(void *ptr)
 {
         return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);
@@ -1104,6 +1109,120 @@ static inline void __set_iter_shift(struct radix_tree_iter *iter,
 #endif
 }
 
+/* Construct iter->tags bit-mask from node->tags[tag] array */
+static void set_iter_tags(struct radix_tree_iter *iter,
+                                struct radix_tree_node *node, unsigned offset,
+                                unsigned tag)
+{
+        unsigned tag_long = offset / BITS_PER_LONG;
+        unsigned tag_bit  = offset % BITS_PER_LONG;
+
+        iter->tags = node->tags[tag][tag_long] >> tag_bit;
+
+        /* This never happens if RADIX_TREE_TAG_LONGS == 1 */
+        if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
+                /* Pick tags from next element */
+                if (tag_bit)
+                        iter->tags |= node->tags[tag][tag_long + 1] <<
+                                                (BITS_PER_LONG - tag_bit);
+                /* Clip chunk size, here only BITS_PER_LONG tags */
+                iter->next_index = __radix_tree_iter_add(iter, BITS_PER_LONG);
+        }
+}
+
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+static void **skip_siblings(struct radix_tree_node **nodep,
+                        void **slot, struct radix_tree_iter *iter)
+{
+        void *sib = node_to_entry(slot - 1);
+
+        while (iter->index < iter->next_index) {
+                *nodep = rcu_dereference_raw(*slot);
+                if (*nodep && *nodep != sib)
+                        return slot;
+                slot++;
+                iter->index = __radix_tree_iter_add(iter, 1);
+                iter->tags >>= 1;
+        }
+
+        *nodep = NULL;
+        return NULL;
+}
+
+void ** __radix_tree_next_slot(void **slot, struct radix_tree_iter *iter,
+                                        unsigned flags)
+{
+        unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
+        struct radix_tree_node *node = rcu_dereference_raw(*slot);
+
+        slot = skip_siblings(&node, slot, iter);
+
+        while (radix_tree_is_internal_node(node)) {
+                unsigned offset;
+                unsigned long next_index;
+
+                if (node == RADIX_TREE_RETRY)
+                        return slot;
+                node = entry_to_node(node);
+                iter->shift = node->shift;
+
+                if (flags & RADIX_TREE_ITER_TAGGED) {
+                        offset = radix_tree_find_next_bit(node, tag, 0);
+                        if (offset == RADIX_TREE_MAP_SIZE)
+                                return NULL;
+                        slot = &node->slots[offset];
+                        iter->index = __radix_tree_iter_add(iter, offset);
+                        set_iter_tags(iter, node, offset, tag);
+                        node = rcu_dereference_raw(*slot);
+                } else {
+                        offset = 0;
+                        slot = &node->slots[0];
+                        for (;;) {
+                                node = rcu_dereference_raw(*slot);
+                                if (node)
+                                        break;
+                                slot++;
+                                offset++;
+                                if (offset == RADIX_TREE_MAP_SIZE)
+                                        return NULL;
+                        }
+                        iter->index = __radix_tree_iter_add(iter, offset);
+                }
+                if ((flags & RADIX_TREE_ITER_CONTIG) && (offset > 0))
+                        goto none;
+                next_index = (iter->index | shift_maxindex(iter->shift)) + 1;
+                if (next_index < iter->next_index)
+                        iter->next_index = next_index;
+        }
+
+        return slot;
+ none:
+        iter->next_index = 0;
+        return NULL;
+}
+EXPORT_SYMBOL(__radix_tree_next_slot);
+#else
+static void **skip_siblings(struct radix_tree_node **nodep,
+                        void **slot, struct radix_tree_iter *iter)
+{
+        return slot;
+}
+#endif
+
+void **radix_tree_iter_resume(void **slot, struct radix_tree_iter *iter)
+{
+        struct radix_tree_node *node;
+
+        slot++;
+        iter->index = __radix_tree_iter_add(iter, 1);
+        node = rcu_dereference_raw(*slot);
+        skip_siblings(&node, slot, iter);
+        iter->next_index = iter->index;
+        iter->tags = 0;
+        return NULL;
+}
+EXPORT_SYMBOL(radix_tree_iter_resume);
+
 /**
  * radix_tree_next_chunk - find next chunk of slots for iteration
  *
@@ -1191,23 +1310,8 @@ void **radix_tree_next_chunk(struct radix_tree_root *root,
         iter->next_index = (index | node_maxindex(node)) + 1;
         __set_iter_shift(iter, node->shift);
 
-        /* Construct iter->tags bit-mask from node->tags[tag] array */
-        if (flags & RADIX_TREE_ITER_TAGGED) {
-                unsigned tag_long, tag_bit;
-
-                tag_long = offset / BITS_PER_LONG;
-                tag_bit  = offset % BITS_PER_LONG;
-                iter->tags = node->tags[tag][tag_long] >> tag_bit;
-                /* This never happens if RADIX_TREE_TAG_LONGS == 1 */
-                if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
-                        /* Pick tags from next element */
-                        if (tag_bit)
-                                iter->tags |= node->tags[tag][tag_long + 1] <<
-                                                (BITS_PER_LONG - tag_bit);
-                        /* Clip chunk size, here only BITS_PER_LONG tags */
-                        iter->next_index = index + BITS_PER_LONG;
-                }
-        }
+        if (flags & RADIX_TREE_ITER_TAGGED)
+                set_iter_tags(iter, node, offset, tag);
 
         return node->slots + offset;
 }
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 7434a63cac94..e32389a97030 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1446,7 +1446,7 @@ static void collapse_shmem(struct mm_struct *mm,
                 radix_tree_replace_slot(&mapping->page_tree, slot,
                                 new_page + (index % HPAGE_PMD_NR));
 
-                slot = radix_tree_iter_next(&iter);
+                slot = radix_tree_iter_resume(slot, &iter);
                 index++;
                 continue;
 out_lru:
@@ -1546,7 +1546,6 @@ tree_unlocked:
                                 /* Put holes back where they were */
                                 radix_tree_delete(&mapping->page_tree,
                                                   iter.index);
-                                slot = radix_tree_iter_next(&iter);
                                 continue;
                         }
 
@@ -1557,11 +1556,11 @@ tree_unlocked:
                         page_ref_unfreeze(page, 2);
                         radix_tree_replace_slot(&mapping->page_tree,
                                                 slot, page);
+                        slot = radix_tree_iter_resume(slot, &iter);
                         spin_unlock_irq(&mapping->tree_lock);
                         putback_lru_page(page);
                         unlock_page(page);
                         spin_lock_irq(&mapping->tree_lock);
-                        slot = radix_tree_iter_next(&iter);
                 }
                 VM_BUG_ON(nr_none);
                 spin_unlock_irq(&mapping->tree_lock);
@@ -1641,8 +1640,8 @@ static void khugepaged_scan_shmem(struct mm_struct *mm,
                 present++;
 
                 if (need_resched()) {
+                        slot = radix_tree_iter_resume(slot, &iter);
                         cond_resched_rcu();
-                        slot = radix_tree_iter_next(&iter);
                 }
         }
         rcu_read_unlock();
diff --git a/mm/shmem.c b/mm/shmem.c
index abd7403aba41..be11c6dd414a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -661,8 +661,8 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
                         swapped++;
 
                 if (need_resched()) {
+                        slot = radix_tree_iter_resume(slot, &iter);
                         cond_resched_rcu();
-                        slot = radix_tree_iter_next(&iter);
                 }
         }
 
@@ -2447,8 +2447,8 @@ static void shmem_tag_pins(struct address_space *mapping)
                 }
 
                 if (need_resched()) {
+                        slot = radix_tree_iter_resume(slot, &iter);
                         cond_resched_rcu();
-                        slot = radix_tree_iter_next(&iter);
                 }
         }
         rcu_read_unlock();
@@ -2517,8 +2517,8 @@ static int shmem_wait_for_pins(struct address_space *mapping)
                         spin_unlock_irq(&mapping->tree_lock);
 continue_resched:
                         if (need_resched()) {
+                                slot = radix_tree_iter_resume(slot, &iter);
                                 cond_resched_rcu();
-                                slot = radix_tree_iter_next(&iter);
                         }
                 }
                 rcu_read_unlock();
diff --git a/tools/testing/radix-tree/iteration_check.c b/tools/testing/radix-tree/iteration_check.c
index df71cb841385..f328a66899b4 100644
--- a/tools/testing/radix-tree/iteration_check.c
+++ b/tools/testing/radix-tree/iteration_check.c
@@ -48,8 +48,8 @@ static void *add_entries_fn(void *arg)
 /*
  * Iterate over the tagged entries, doing a radix_tree_iter_retry() as we find
  * things that have been removed and randomly resetting our iteration to the
- * next chunk with radix_tree_iter_next().  Both radix_tree_iter_retry() and
- * radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
+ * next chunk with radix_tree_iter_resume().  Both radix_tree_iter_retry() and
+ * radix_tree_iter_resume() cause radix_tree_next_slot() to be called with a
  * NULL 'slot' variable.
  */
 static void *tagged_iteration_fn(void *arg)
@@ -79,7 +79,7 @@ static void *tagged_iteration_fn(void *arg)
                         }
 
                         if (rand_r(&seeds[0]) % 50 == 0) {
-                                slot = radix_tree_iter_next(&iter);
+                                slot = radix_tree_iter_resume(slot, &iter);
                                 rcu_read_unlock();
                                 rcu_barrier();
                                 rcu_read_lock();
@@ -96,8 +96,8 @@ static void *tagged_iteration_fn(void *arg)
 /*
  * Iterate over the entries, doing a radix_tree_iter_retry() as we find things
  * that have been removed and randomly resetting our iteration to the next
- * chunk with radix_tree_iter_next().  Both radix_tree_iter_retry() and
- * radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
+ * chunk with radix_tree_iter_resume().  Both radix_tree_iter_retry() and
+ * radix_tree_iter_resume() cause radix_tree_next_slot() to be called with a
  * NULL 'slot' variable.
  */
 static void *untagged_iteration_fn(void *arg)
@@ -127,7 +127,7 @@ static void *untagged_iteration_fn(void *arg)
                         }
 
                         if (rand_r(&seeds[1]) % 50 == 0) {
-                                slot = radix_tree_iter_next(&iter);
+                                slot = radix_tree_iter_resume(slot, &iter);
                                 rcu_read_unlock();
                                 rcu_barrier();
                                 rcu_read_lock();
diff --git a/tools/testing/radix-tree/multiorder.c b/tools/testing/radix-tree/multiorder.c
index 8d5865c95664..b9be8856d652 100644
--- a/tools/testing/radix-tree/multiorder.c
+++ b/tools/testing/radix-tree/multiorder.c
@@ -231,11 +231,14 @@ void multiorder_iteration(void)
                 radix_tree_for_each_slot(slot, &tree, &iter, j) {
                         int height = order[i] / RADIX_TREE_MAP_SHIFT;
                         int shift = height * RADIX_TREE_MAP_SHIFT;
-                        int mask = (1 << order[i]) - 1;
+                        unsigned long mask = (1UL << order[i]) - 1;
+                        struct item *item = *slot;
 
-                        assert(iter.index >= (index[i] &~ mask));
-                        assert(iter.index <= (index[i] | mask));
+                        assert((iter.index | mask) == (index[i] | mask));
                         assert(iter.shift == shift);
+                        assert(!radix_tree_is_internal_node(item));
+                        assert((item->index | mask) == (index[i] | mask));
+                        assert(item->order == order[i]);
                         i++;
                 }
         }
@@ -269,7 +272,7 @@ void multiorder_tagged_iteration(void)
                 assert(radix_tree_tag_set(&tree, tag_index[i], 1));
 
         for (j = 0; j < 256; j++) {
-                int mask, k;
+                int k;
 
                 for (i = 0; i < TAG_ENTRIES; i++) {
                         for (k = i; index[k] < tag_index[i]; k++)
@@ -279,12 +282,16 @@ void multiorder_tagged_iteration(void)
                 }
 
                 radix_tree_for_each_tagged(slot, &tree, &iter, j, 1) {
+                        unsigned long mask;
+                        struct item *item = *slot;
                         for (k = i; index[k] < tag_index[i]; k++)
                                 ;
-                        mask = (1 << order[k]) - 1;
+                        mask = (1UL << order[k]) - 1;
 
-                        assert(iter.index >= (tag_index[i] &~ mask));
-                        assert(iter.index <= (tag_index[i] | mask));
+                        assert((iter.index | mask) == (tag_index[i] | mask));
+                        assert(!radix_tree_is_internal_node(item));
+                        assert((item->index | mask) == (tag_index[i] | mask));
+                        assert(item->order == order[k]);
                         i++;
                 }
         }
@@ -303,12 +310,15 @@ void multiorder_tagged_iteration(void)
                 }
 
                 radix_tree_for_each_tagged(slot, &tree, &iter, j, 2) {
+                        struct item *item = *slot;
                         for (k = i; index[k] < tag_index[i]; k++)
                                 ;
                         mask = (1 << order[k]) - 1;
 
-                        assert(iter.index >= (tag_index[i] &~ mask));
-                        assert(iter.index <= (tag_index[i] | mask));
+                        assert((iter.index | mask) == (tag_index[i] | mask));
+                        assert(!radix_tree_is_internal_node(item));
+                        assert((item->index | mask) == (tag_index[i] | mask));
+                        assert(item->order == order[k]);
                         i++;
                 }
         }
diff --git a/tools/testing/radix-tree/regression3.c b/tools/testing/radix-tree/regression3.c
index 1f06ed73d0a8..b594841fae85 100644
--- a/tools/testing/radix-tree/regression3.c
+++ b/tools/testing/radix-tree/regression3.c
@@ -5,7 +5,7 @@
  * In following radix_tree_next_slot current chunk size becomes zero.
  * This isn't checked and it tries to dereference null pointer in slot.
  *
- * Helper radix_tree_iter_next reset slot to NULL and next_index to index + 1,
+ * Helper radix_tree_iter_resume reset slot to NULL and next_index to index + 1,
  * for tagger iteraction it also must reset cached tags in iterator to abort
  * next radix_tree_next_slot and go to slow-path into radix_tree_next_chunk.
  *
@@ -88,7 +88,7 @@ void regression3_test(void)
                 printf("slot %ld %p\n", iter.index, *slot);
                 if (!iter.index) {
                         printf("next at %ld\n", iter.index);
-                        slot = radix_tree_iter_next(&iter);
+                        slot = radix_tree_iter_resume(slot, &iter);
                 }
         }
 
@@ -96,7 +96,7 @@ void regression3_test(void)
                 printf("contig %ld %p\n", iter.index, *slot);
                 if (!iter.index) {
                         printf("next at %ld\n", iter.index);
-                        slot = radix_tree_iter_next(&iter);
+                        slot = radix_tree_iter_resume(slot, &iter);
                 }
         }
 
@@ -106,7 +106,7 @@ void regression3_test(void)
                 printf("tagged %ld %p\n", iter.index, *slot);
                 if (!iter.index) {
                         printf("next at %ld\n", iter.index);
-                        slot = radix_tree_iter_next(&iter);
+                        slot = radix_tree_iter_resume(slot, &iter);
                 }
         }
 
diff --git a/tools/testing/radix-tree/test.h b/tools/testing/radix-tree/test.h
index 423c528aaee9..617416ec3c5e 100644
--- a/tools/testing/radix-tree/test.h
+++ b/tools/testing/radix-tree/test.h
@@ -41,6 +41,7 @@ void verify_tag_consistency(struct radix_tree_root *root, unsigned int tag);
 extern int nr_allocated;
 
 /* Normally private parts of lib/radix-tree.c */
+struct radix_tree_node *entry_to_node(void *ptr);
 void radix_tree_dump(struct radix_tree_root *root);
 int root_tag_get(struct radix_tree_root *root, unsigned int tag);
 unsigned long node_maxindex(struct radix_tree_node *);