linux-kernel - Re: [PATCH v2] maple_tree: Add lockdep assertion in mas_dup

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Message-ID: <20260121135238.26578-1-boudewijn@delta-utec.com>
Date: Wed, 21 Jan 2026 14:52:38 +0100
From: Boudewijn van der Heide <boudewijn@...ta-utec.com>
To: liam.howlett@...cle.com
Cc: akpm@...ux-foundation.org,
	aliceryhl@...gle.com,
	andrewjballance@...il.com,
	boudewijn@...ta-utec.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	maple-tree@...ts.infradead.org
Subject: Re: [PATCH v2] maple_tree: Add lockdep assertion in mas_dup_alloc()

Thanks for the review! That makes sense, I overlooked this detail in v2.
We should absolutely just check in __mt_dup(),
like mtree_dup() does for actual locks.
I took a closer look at __mt_dup() and mtree_dup(),
and I saw that mtree_dup() locks both the new and old maple_tree.
So I think it also makes sense for us to assert both trees in __mt_dup(),
like this:

@@ -6379,6 +6379,9 @@ int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
 	MA_STATE(mas, mt, 0, 0);
 	MA_STATE(new_mas, new, 0, 0);
 
+	lockdep_assert(mt_write_locked(new));
+	lockdep_assert(mt_write_locked(mt));
+
 	mas_dup_build(&mas, &new_mas, gfp);
 	if (unlikely(mas_is_err(&mas))) {
 		ret = xa_err(mas.node);

Does that look good to you for v3?

> >  	/* Allocate memory for child nodes. */
> >  	type = mte_node_type(mas->node);
> >  	new_slots = ma_slots(new_node, type);
> > --
> > 2.47.3
> > 
> >
> 

Thanks,
Boudewijn