The patch titled Subject: maple_tree: remove rcu_read_lock() from mt_validate() has been added to the -mm mm-hotfixes-unstable branch. Its filename is maple_tree-remove-rcu_read_lock-from-mt_validate.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Liam R. Howlett" Liam.Howlett@Oracle.com Subject: maple_tree: remove rcu_read_lock() from mt_validate() Date: Tue, 20 Aug 2024 13:54:17 -0400

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 ---

lib/maple_tree.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/lib/maple_tree.c~maple_tree-remove-rcu_read_lock-from-mt_validate +++ a/lib/maple_tree.c @@ -7566,14 +7566,14 @@ 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); @@ -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);

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Patches currently in -mm which might be from Liam.Howlett@Oracle.com are

maple_tree-remove-rcu_read_lock-from-mt_validate.patch