linux-kernel - [PATCH 1/2] maple_tree: check for MA_STATE_BULK on setting wr

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Message-ID: <20241011214451.7286-1-sidhartha.kumar@oracle.com>
Date: Fri, 11 Oct 2024 17:44:50 -0400
From: Sidhartha Kumar <sidhartha.kumar@...cle.com>
To: linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, liam.howlett@...cle.com,
        willy@...radead.org, richard.weiyang@...il.com,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>
Subject: [PATCH 1/2] maple_tree: check for MA_STATE_BULK on setting wr_rebalance

It is possible for a bulk operation (MA_STATE_BULK is set) to enter the
new_end < mt_min_slots[type] case and set wr_rebalance as a store type.
This is incorrect as bulk stores do not rebalance per write, but rather
after the all of the writes are done through the mas_bulk_rebalance()
path. Therefore, add a check to make sure MA_STATE_BULK is not set
before we return wr_rebalance as the store type.

Also add a test to make sure wr_rebalance is never the store type when
doing bulk operations via mas_expected_entries()

Fixes: 5d659bbb52a2 ("maple_tree: introduce mas_wr_store_type()")
Suggested-by: Liam Howlett <liam.howlett@...cle.com>
Signed-off-by: Sidhartha <sidhartha.kumar@...cle.com>
---

Hi Andrew, this commit is a hotfix for this rc however it has no userspace
effects as there are no users of the bulk instertion mode.

 lib/maple_tree.c                 |  2 +-
 tools/testing/radix-tree/maple.c | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 4b423330d83c..b3b1d4b8126b 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4228,7 +4228,7 @@ static inline void mas_wr_store_type(struct ma_wr_state *wr_mas)
 
 	/* Potential spanning rebalance collapsing a node */
 	if (new_end < mt_min_slots[wr_mas->type]) {
-		if (!mte_is_root(mas->node)) {
+		if (!mte_is_root(mas->node) && !(mas->mas_flags & MA_STATE_BULK)) {
 			mas->store_type = wr_rebalance;
 			return;
 		}
diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index 5fde09999be4..551ae6898c1d 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -36317,6 +36317,28 @@ static inline int check_vma_modification(struct maple_tree *mt)
 	return 0;
 }
 
+/*
+ * test to check that bulk stores do not use wr_rebalance as the store
+ * type.
+ */
+static inline void check_bulk_rebalance(struct maple_tree *mt)
+{
+	MA_STATE(mas, mt, ULONG_MAX, ULONG_MAX);
+	int max = 10;
+
+	build_full_tree(mt, 0, 2);
+
+	/* erase every entry in the tree */
+	do {
+		/* set up bulk store mode */
+		mas_expected_entries(&mas, max);
+		mas_erase(&mas);
+		MT_BUG_ON(mt, mas.store_type == wr_rebalance);
+	} while (mas_prev(&mas, 0) != NULL);
+
+	mas_destroy(&mas);
+}
+
 void farmer_tests(void)
 {
 	struct maple_node *node;
@@ -36328,6 +36350,10 @@ void farmer_tests(void)
 	check_vma_modification(&tree);
 	mtree_destroy(&tree);
 
+	mt_init(&tree);
+	check_bulk_rebalance(&tree);
+	mtree_destroy(&tree);
+
 	tree.ma_root = xa_mk_value(0);
 	mt_dump(&tree, mt_dump_dec);
 
-- 
2.43.0