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From:   "Liam R. Howlett" <Liam.Howlett@oracle.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org
Cc:     maple-tree@lists.infradead.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        Stable@vger.kernel.org, Liam Howlett <Liam.Howlett@oracle.com>
Subject: [PATCH 6.1 09/14] maple_tree: detect dead nodes in mas_start()
Date:   Tue, 11 Apr 2023 11:10:50 -0400
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From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

commit a7b92d59c885018cb7bb88539892278e4fd64b29 upstream.

When initially starting a search, the root node may already be in the
process of being replaced in RCU mode.  Detect and restart the walk if
this is the case.  This is necessary for RCU mode of the maple tree.

Link: https://lkml.kernel.org/r/20230227173632.3292573-3-surenb@google.com
Cc: <Stable@vger.kernel.org>
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam Howlett <Liam.Howlett@oracle.com>
---
 lib/maple_tree.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 194963149c2d..6fcf08dbdbf9 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1352,12 +1352,16 @@ static inline struct maple_enode *mas_start(struct ma_state *mas)
 		mas->max = ULONG_MAX;
 		mas->depth = 0;
 
+retry:
 		root = mas_root(mas);
 		/* Tree with nodes */
 		if (likely(xa_is_node(root))) {
 			mas->depth = 1;
 			mas->node = mte_safe_root(root);
 			mas->offset = 0;
+			if (mte_dead_node(mas->node))
+				goto retry;
+
 			return NULL;
 		}
 
-- 
2.39.2