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/maple_tree-remove-rcu_read_lock-from-mt_validate.patch
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@xxxxxxxxxx>
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@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>
---
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);
_
Patches currently in -mm which might be from Liam.Howlett@xxxxxxxxxx are
maple_tree-remove-rcu_read_lock-from-mt_validate.patch
