linux-kernel - Re: [PATCH v2 1/3] testing/radix-tree/maple: Hack around kfree

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Message-ID: <erokvcuas3jqy3t4j2kjui47os4kph46swl5pjcrj5kd6lazlp@2epxbn57v6y4>
Date: Tue, 12 Aug 2025 15:41:35 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Pedro Falcato <pfalcato@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, maple-tree@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v2 1/3] testing/radix-tree/maple: Hack around kfree_rcu
 not existing

* Pedro Falcato <pfalcato@...e.de> [250812 12:21]:
> liburcu doesn't have kfree_rcu (or anything similar). Despite that, we
> can hack around it in a trivial fashion, by adding a wrapper.
> 
> This wrapper only works for maple_nodes, and not anything else (due to
> us not being able to know rcu_head offsets in any way), and thus we take
> advantage of the type checking to avoid future silent breakage.
> 
> Reviewed-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> Signed-off-by: Pedro Falcato <pfalcato@...e.de>
> ---
> v2:
>  - Move kfree_rcu hack to maple-shared.h, to fix userland VMA tests, per
>    Lorenzo

This is going to cause issues with sheaves that's probably going to go
through vlastimil's branch.

We're going to either get this to go through there with some
modification to avoid conflict, or we're going to hold off for now.


> 
>  tools/testing/shared/maple-shared.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/tools/testing/shared/maple-shared.h b/tools/testing/shared/maple-shared.h
> index dc4d30f3860b..572cd2580123 100644
> --- a/tools/testing/shared/maple-shared.h
> +++ b/tools/testing/shared/maple-shared.h
> @@ -9,5 +9,20 @@
>  #include <stdlib.h>
>  #include <time.h>
>  #include "linux/init.h"
> +#include <linux/maple_tree.h>
> +
> +static inline void free_node(struct rcu_head *head)
> +{
> +	struct maple_node *node = container_of(head, struct maple_node, rcu);
> +
> +	free(node);
> +}
> +
> +static inline void kfree_rcu_node(struct maple_node *node)
> +{
> +	call_rcu(&node->rcu, free_node);
> +}
> +
> +#define kfree_rcu(ptr, memb) kfree_rcu_node(ptr)
>  
>  #endif /* __MAPLE_SHARED_H__ */
> -- 
> 2.50.1
>