linux-kernel - [PATCH v2 01/29] maple_tree: Fix mas_dup

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Message-ID: <20260121164526.2093265-2-Liam.Howlett@oracle.com>
Date: Wed, 21 Jan 2026 11:44:58 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Alice Ryhl <aliceryhl@...gle.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>, Christian Kujau <lists@...dbynature.de>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v2 01/29] maple_tree: Fix mas_dup_alloc() sparse warning

Use RCU_INIT_POINTER to initialize an rcu pointer to an initial value
since there are no readers within the tree being created during
duplication.  There is no risk of readers seeing the initialized or
uninitialized value until after the synchronization call in
mas_dup_buld().

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 lib/maple_tree.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 5aa4c95000188..0e0158ee7ba55 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -6260,8 +6260,15 @@ static inline void mas_dup_alloc(struct ma_state *mas, struct ma_state *new_mas,
 	for (i = 0; i < count; i++) {
 		val = (unsigned long)mt_slot_locked(mas->tree, slots, i);
 		val &= MAPLE_NODE_MASK;
-		new_slots[i] = ma_mnode_ptr((unsigned long)mas_pop_node(mas) |
-					    val);
+		/*
+		 * Warning, see rcu_assign_pointer() documentation.  Since this
+		 * is a duplication of a tree, there are no readers walking the
+		 * tree until after the rcu_assign_pointer() call in
+		 * mas_dup_build().
+		 */
+		RCU_INIT_POINTER(new_slots[i],
+				 ma_mnode_ptr((unsigned long)mas_pop_node(mas) |
+					      val));
 	}
 }
 
-- 
2.47.3