FROMGIT: maple_tree: introduce mas_next_slot() interface

Sometimes, during a tree walk, the user needs the next slot regardless of
if it is empty or not.  Add an interface to get the next slot.

Since there are no consecutive NULLs allowed in the tree, the mas_next()
function can only advance two slots at most.  So use the new
mas_next_slot() interface to align both implementations.  Use this method
for mas_find() as well.

Link: https://lkml.kernel.org/r/20230518145544.1722059-28-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit d0e70747bdb8f9cfc9ff48474e83171587ad94c1
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm mm-unstable)

Bug: 274059236
Change-Id: I9efc69267859c26aae1b776d103dff584f1961ea
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

lib/maple_tree.c

@@ -4634,11 +4634,10 @@ no_entry:
 static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 				unsigned long max)
 {
-	unsigned long min, pivot;
+	unsigned long min;
 	unsigned long *pivots;
 	struct maple_enode *enode;
 	int level = 0;
-	unsigned char offset;
 	unsigned char node_end;
 	enum maple_type mt;
 	void __rcu **slots;
@@ -4646,19 +4645,16 @@ static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 	if (mas->max >= max)
 		goto no_entry;
 
+	min = mas->max + 1;
 	level = 0;
 	do {
 		if (ma_is_root(node))
 			goto no_entry;
 
-		min = mas->max + 1;
+		/* Walk up. */
-		if (min > max)
-			goto no_entry;
-
 		if (unlikely(mas_ascend(mas)))
 			return 1;
 
-		offset = mas->offset;
 		level++;
 		node = mas_mn(mas);
 		mt = mte_node_type(mas->node);
@@ -4667,36 +4663,37 @@ static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 		if (unlikely(ma_dead_node(node)))
 			return 1;
 
-	} while (unlikely(offset == node_end));
+	} while (unlikely(mas->offset == node_end));
 
 	slots = ma_slots(node, mt);
-	pivot = mas_safe_pivot(mas, pivots, ++offset, mt);
+	mas->offset++;
-	while (unlikely(level > 1)) {
+	enode = mas_slot(mas, slots, mas->offset);
-		/* Descend, if necessary */
+	if (unlikely(ma_dead_node(node)))
-		enode = mas_slot(mas, slots, offset);
+		return 1;
-		if (unlikely(ma_dead_node(node)))
-			return 1;
 
-		mas->node = enode;
+	if (level > 1)
+		mas->offset = 0;
+
+	while (unlikely(level > 1)) {
 		level--;
+		mas->node = enode;
 		node = mas_mn(mas);
 		mt = mte_node_type(mas->node);
 		slots = ma_slots(node, mt);
-		pivots = ma_pivots(node, mt);
+		enode = mas_slot(mas, slots, 0);
 		if (unlikely(ma_dead_node(node)))
 			return 1;
-
-		offset = 0;
-		pivot = pivots[0];
 	}
 
-	enode = mas_slot(mas, slots, offset);
+	if (!mas->offset)
+		pivots = ma_pivots(node, mt);
+
+	mas->max = mas_safe_pivot(mas, pivots, mas->offset, mt);
 	if (unlikely(ma_dead_node(node)))
 		return 1;
 
 	mas->node = enode;
 	mas->min = min;
-	mas->max = pivot;
 	return 0;
 
 no_entry:
@@ -4707,76 +4704,6 @@ no_entry:
 	return 0;
 }
 
-/*
- * mas_next_nentry() - Get the next node entry
- * @mas: The maple state
- * @max: The maximum value to check
- * @*range_start: Pointer to store the start of the range.
- *
- * Sets @mas->offset to the offset of the next node entry, @mas->last to the
- * pivot of the entry.
- *
- * Return: The next entry, %NULL otherwise
- */
-static inline void *mas_next_nentry(struct ma_state *mas,
-	    struct maple_node *node, unsigned long max, enum maple_type type)
-{
-	unsigned char count;
-	unsigned long pivot;
-	unsigned long *pivots;
-	void __rcu **slots;
-	void *entry;
-
-	if (mas->last == mas->max) {
-		mas->index = mas->max;
-		return NULL;
-	}
-
-	slots = ma_slots(node, type);
-	pivots = ma_pivots(node, type);
-	count = ma_data_end(node, type, pivots, mas->max);
-	if (unlikely(ma_dead_node(node)))
-		return NULL;
-
-	mas->index = mas_safe_min(mas, pivots, mas->offset);
-	if (unlikely(ma_dead_node(node)))
-		return NULL;
-
-	if (mas->index > max)
-		return NULL;
-
-	if (mas->offset > count)
-		return NULL;
-
-	while (mas->offset < count) {
-		pivot = pivots[mas->offset];
-		entry = mas_slot(mas, slots, mas->offset);
-		if (ma_dead_node(node))
-			return NULL;
-
-		mas->last = pivot;
-		if (entry)
-			return entry;
-
-		if (pivot >= max)
-			return NULL;
-
-		if (pivot >= mas->max)
-			return NULL;
-
-		mas->index = pivot + 1;
-		mas->offset++;
-	}
-
-	pivot = mas_logical_pivot(mas, pivots, mas->offset, type);
-	entry = mas_slot(mas, slots, mas->offset);
-	if (ma_dead_node(node))
-		return NULL;
-
-	mas->last = pivot;
-	return entry;
-}
-
 static inline void mas_rewalk(struct ma_state *mas, unsigned long index)
 {
 
@@ -4785,9 +4712,99 @@ retry:
 	mas_state_walk(mas);
 	if (mas_is_start(mas))
 		goto retry;
+}
 
-	return;
+static inline bool mas_rewalk_if_dead(struct ma_state *mas,
+		struct maple_node *node, const unsigned long index)
+{
+	if (unlikely(ma_dead_node(node))) {
+		mas_rewalk(mas, index);
+		return true;
+	}
+	return false;
+}
 
+/*
+ * mas_next_slot() - Get the entry in the next slot
+ *
+ * @mas: The maple state
+ * @max: The maximum starting range
+ * @empty: Can be empty
+ *
+ * Return: The entry in the next slot which is possibly NULL
+ */
+void *mas_next_slot(struct ma_state *mas, unsigned long max, bool empty)
+{
+	void __rcu **slots;
+	unsigned long *pivots;
+	unsigned long pivot;
+	enum maple_type type;
+	struct maple_node *node;
+	unsigned char data_end;
+	unsigned long save_point = mas->last;
+	void *entry;
+
+retry:
+	node = mas_mn(mas);
+	type = mte_node_type(mas->node);
+	pivots = ma_pivots(node, type);
+	data_end = ma_data_end(node, type, pivots, mas->max);
+	if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
+		goto retry;
+
+again:
+	if (mas->max >= max) {
+		if (likely(mas->offset < data_end))
+			pivot = pivots[mas->offset];
+		else
+			return NULL; /* must be mas->max */
+
+		if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
+			goto retry;
+
+		if (pivot >= max)
+			return NULL;
+	}
+
+	if (likely(mas->offset < data_end)) {
+		mas->index = pivots[mas->offset] + 1;
+		mas->offset++;
+		if (likely(mas->offset < data_end))
+			mas->last = pivots[mas->offset];
+		else
+			mas->last = mas->max;
+	} else  {
+		if (mas_next_node(mas, node, max)) {
+			mas_rewalk(mas, save_point);
+			goto retry;
+		}
+
+		if (mas_is_none(mas))
+			return NULL;
+
+		mas->offset = 0;
+		mas->index = mas->min;
+		node = mas_mn(mas);
+		type = mte_node_type(mas->node);
+		pivots = ma_pivots(node, type);
+		mas->last = pivots[0];
+	}
+
+	slots = ma_slots(node, type);
+	entry = mt_slot(mas->tree, slots, mas->offset);
+	if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
+		goto retry;
+
+	if (entry)
+		return entry;
+
+	if (!empty) {
+		if (!mas->offset)
+			data_end = 2;
+		goto again;
+	}
+
+	return entry;
 }
 
 /*
@@ -4805,47 +4822,12 @@ retry:
 static inline void *mas_next_entry(struct ma_state *mas, unsigned long limit)
 {
 	void *entry = NULL;
-	struct maple_node *node;
-	unsigned long last;
-	enum maple_type mt;
 
 	if (mas->last >= limit)
 		return NULL;
 
-	last = mas->last;
+	entry = mas_next_slot(mas, limit, false);
-retry:
+	return entry;
-	node = mas_mn(mas);
-	mt = mte_node_type(mas->node);
-	mas->offset++;
-	if (unlikely(mas->offset >= mt_slots[mt])) {
-		mas->offset = mt_slots[mt] - 1;
-		goto next_node;
-	}
-
-	while (!mas_is_none(mas)) {
-		entry = mas_next_nentry(mas, node, limit, mt);
-		if (unlikely(ma_dead_node(node))) {
-			mas_rewalk(mas, last);
-			goto retry;
-		}
-
-		if (likely(entry))
-			return entry;
-
-		if (unlikely((mas->last >= limit)))
-			return NULL;
-
-next_node:
-		if (unlikely(mas_next_node(mas, node, limit))) {
-			mas_rewalk(mas, last);
-			goto retry;
-		}
-		mas->offset = 0;
-		node = mas_mn(mas);
-		mt = mte_node_type(mas->node);
-	}
-
-	return NULL;
 }
 
 /*
@@ -4876,10 +4858,8 @@ retry:
 	slots = ma_slots(mn, mt);
 	pivots = ma_pivots(mn, mt);
 	count = ma_data_end(mn, mt, pivots, mas->max);
-	if (unlikely(ma_dead_node(mn))) {
+	if (unlikely(mas_rewalk_if_dead(mas, mn, index)))
-		mas_rewalk(mas, index);
 		goto retry;
-	}
 
 	offset = mas->offset - 1;
 	if (offset >= mt_slots[mt])
@@ -4892,10 +4872,8 @@ retry:
 		pivot = pivots[offset];
 	}
 
-	if (unlikely(ma_dead_node(mn))) {
+	if (unlikely(mas_rewalk_if_dead(mas, mn, index)))
-		mas_rewalk(mas, index);
 		goto retry;
-	}
 
 	while (offset && !mas_slot(mas, slots, offset)) {
 		pivot = pivots[--offset];
@@ -4912,10 +4890,8 @@ retry:
 
 	min = mas_safe_min(mas, pivots, offset);
 	entry = mas_slot(mas, slots, offset);
-	if (unlikely(ma_dead_node(mn))) {
+	if (unlikely(mas_rewalk_if_dead(mas, mn, index)))
-		mas_rewalk(mas, index);
 		goto retry;
-	}
 
 	mas->offset = offset;
 	mas->last = pivot;
@@ -6181,8 +6157,8 @@ void *mas_find(struct ma_state *mas, unsigned long max)
 	if (mas->index == max)
 		return NULL;
 
-	/* Retries on dead nodes handled by mas_next_entry */
+	/* Retries on dead nodes handled by mas_next_slot */
-	return mas_next_entry(mas, max);
+	return mas_next_slot(mas, max, false);
 
 ptr_out_of_range:
 	mas->node = MAS_NONE;