[PATCH 6.10 056/375] maple_tree: remove rcu_read_lock() from mt_validate()

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6.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>

commit f806de88d8f7f8191afd0fd9b94db4cd058e7d4f upstream.

The write lock should be held when validating the tree to avoid updates
racing with checks.  Holding the rcu read lock during a large tree
validation may also cause a prolonged rcu read window and "rcu_preempt
detected stalls" warnings.

Link: https://lore.kernel.org/all/0000000000001d12d4062005aea1@xxxxxxxxxx/
Link: https://lkml.kernel.org/r/20240820175417.2782532-1-Liam.Howlett@xxxxxxxxxx
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reported-by: syzbot+036af2f0c7338a33b0cd@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 lib/maple_tree.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -7569,14 +7569,14 @@ static void mt_validate_nulls(struct map
  * 2. The gap is correctly set in the parents
  */
 void mt_validate(struct maple_tree *mt)
+	__must_hold(mas->tree->ma_lock)
 {
 	unsigned char end;
 
 	MA_STATE(mas, mt, 0, 0);
-	rcu_read_lock();
 	mas_start(&mas);
 	if (!mas_is_active(&mas))
-		goto done;
+		return;
 
 	while (!mte_is_leaf(mas.node))
 		mas_descend(&mas);
@@ -7597,9 +7597,6 @@ void mt_validate(struct maple_tree *mt)
 		mas_dfs_postorder(&mas, ULONG_MAX);
 	}
 	mt_validate_nulls(mt);
-done:
-	rcu_read_unlock();
-
 }
 EXPORT_SYMBOL_GPL(mt_validate);
 






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