linux-kernel - [PATCH v2 1/8] maple_tree: set the node limit when creating a new root node

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Message-Id: <20230711035444.526-2-zhangpeng.00@bytedance.com>
Date:   Tue, 11 Jul 2023 11:54:37 +0800
From:   Peng Zhang <zhangpeng.00@...edance.com>
To:     Liam.Howlett@...cle.com
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org,
        Peng Zhang <zhangpeng.00@...edance.com>,
        stable@...r.kernel.org, Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH v2 1/8] maple_tree: set the node limit when creating a new root node

Set the node limit of the root node so that the last pivot of all nodes
is the node limit (if the node is not full).

This patch also fixes a bug in mas_rev_awalk().  Effectively, always
setting a maximum makes mas_logical_pivot() behave as mas_safe_pivot().
Without this fix, it is possible that very small tasks would fail to
find the correct gap.  Although this has not been observed with real
tasks, it has been reported to happen in m68k nommu running the maple
tree tests.

Link: https://lore.kernel.org/linux-mm/CAMuHMdV4T53fOw7VPoBgPR7fP6RYqf=CBhD_y_vOg53zZX_DnA@mail.gmail.com/
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
Cc: <stable@...r.kernel.org>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
---
 lib/maple_tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index d3072858c280..f55e59bd9122 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3692,7 +3692,8 @@ static inline int mas_root_expand(struct ma_state *mas, void *entry)
 	mas->offset = slot;
 	pivots[slot] = mas->last;
 	if (mas->last != ULONG_MAX)
-		slot++;
+		pivots[++slot] = ULONG_MAX;
+
 	mas->depth = 1;
 	mas_set_height(mas);
 	ma_set_meta(node, maple_leaf_64, 0, slot);
-- 
2.20.1