linux-kernel - [PATCH v3 3/4] maple_tree: Fix mas_empty

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Date:   Fri, 21 Apr 2023 09:55:58 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        maple-tree@...ts.infradead.org,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Peng Zhang <zhangpeng.00@...edance.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v3 3/4] maple_tree: Fix mas_empty_area() search

The internal function of mas_awalk() was incorrectly skipping the last
entry in a node, which could potentially be NULL.  This is only a
problem for the left-most node in the tree - otherwise that NULL would
not exist.

Fix mas_awalk() by using the metadata to obtain the end of the node for
the loop and the logical pivot as apposed to the raw pivot value.

Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 lib/maple_tree.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index cf4f6cdcaad38..51910c74d4895 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5029,10 +5029,10 @@ static inline bool mas_anode_descend(struct ma_state *mas, unsigned long size)
 {
 	enum maple_type type = mte_node_type(mas->node);
 	unsigned long pivot, min, gap = 0;
-	unsigned char offset;
-	unsigned long *gaps;
-	unsigned long *pivots = ma_pivots(mas_mn(mas), type);
-	void __rcu **slots = ma_slots(mas_mn(mas), type);
+	unsigned char offset, data_end;
+	unsigned long *gaps, *pivots;
+	void __rcu **slots;
+	struct maple_node *node;
 	bool found = false;
 
 	if (ma_is_dense(type)) {
@@ -5040,13 +5040,15 @@ static inline bool mas_anode_descend(struct ma_state *mas, unsigned long size)
 		return true;
 	}
 
-	gaps = ma_gaps(mte_to_node(mas->node), type);
+	node = mas_mn(mas);
+	pivots = ma_pivots(node, type);
+	slots = ma_slots(node, type);
+	gaps = ma_gaps(node, type);
 	offset = mas->offset;
 	min = mas_safe_min(mas, pivots, offset);
-	for (; offset < mt_slots[type]; offset++) {
-		pivot = mas_safe_pivot(mas, pivots, offset, type);
-		if (offset && !pivot)
-			break;
+	data_end = ma_data_end(node, type, pivots, mas->max);
+	for (; offset <= data_end; offset++) {
+		pivot = mas_logical_pivot(mas, pivots, offset, type);
 
 		/* Not within lower bounds */
 		if (mas->index > pivot)
-- 
2.39.2