maple_tree: remove rcu_read_lock() from mt_validate()

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@google.com/
Link: https://lkml.kernel.org/r/20240820175417.2782532-1-Liam.Howlett@oracle.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reported-by: syzbot+036af2f0c7338a33b0cd@syzkaller.appspotmail.com
Cc: Hillf Danton <hdanton@sina.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index aa3a5df15b8ef926444fb6d8d18b5be4840227e0..6df3a8b95808ab69740bd169a3a07b8edbcfe8c4 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -7566,14 +7566,14 @@ static void mt_validate_nulls(struct maple_tree *mt)
  * 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);
@@ -7594,9 +7594,6 @@ 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);