linux-kernel - Re: [PATCH v8 17/23] testing/radix-tree/maple: Hack around kfree

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Message-ID: <CAJuCfpFrFn01Dx88vYaDnByRraE3qPvO4rfMaortgwYyVsybZg@mail.gmail.com>
Date: Fri, 26 Sep 2025 16:53:43 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Harry Yoo <harry.yoo@...cle.com>, Uladzislau Rezki <urezki@...il.com>, 
	Sidhartha Kumar <sidhartha.kumar@...cle.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, rcu@...r.kernel.org, 
	maple-tree@...ts.infradead.org, Pedro Falcato <pfalcato@...e.de>
Subject: Re: [PATCH v8 17/23] testing/radix-tree/maple: Hack around kfree_rcu
 not existing

On Wed, Sep 10, 2025 at 1:01 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>
> liburcu doesn't have kfree_rcu (or anything similar). Despite that, we
> can hack around it in a trivial fashion, by adding a wrapper.
>
> The wrapper only works for maple_nodes because we cannot get the
> kmem_cache pointer any other way in the test code.
>
> Link: https://lore.kernel.org/all/20250812162124.59417-1-pfalcato@suse.de/
> Suggested-by: Pedro Falcato <pfalcato@...e.de>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

With one nit below:

> ---
>  tools/testing/shared/maple-shared.h | 11 +++++++++++
>  tools/testing/shared/maple-shim.c   |  6 ++++++
>  2 files changed, 17 insertions(+)
>
> diff --git a/tools/testing/shared/maple-shared.h b/tools/testing/shared/maple-shared.h
> index dc4d30f3860b9bd23b4177c7d7926ac686887815..2a1e9a8594a2834326cd9374738b2a2c7c3f9f7c 100644
> --- a/tools/testing/shared/maple-shared.h
> +++ b/tools/testing/shared/maple-shared.h
> @@ -10,4 +10,15 @@
>  #include <time.h>
>  #include "linux/init.h"
>
> +void maple_rcu_cb(struct rcu_head *head);
> +#define rcu_cb         maple_rcu_cb
> +
> +#define kfree_rcu(_struct, _memb)              \
> +do {                                            \
> +    typeof(_struct) _p_struct = (_struct);      \

Maybe add an assertion that (typeof(_struct) == typeof(struct
maple_node)) to make sure kfree_rcu() is not used for anything else in
the tests?

> +                                                \
> +    call_rcu(&((_p_struct)->_memb), rcu_cb);    \
> +} while(0);
> +
> +
>  #endif /* __MAPLE_SHARED_H__ */
> diff --git a/tools/testing/shared/maple-shim.c b/tools/testing/shared/maple-shim.c
> index 9d7b743415660305416e972fa75b56824211b0eb..16252ee616c0489c80490ff25b8d255427bf9fdc 100644
> --- a/tools/testing/shared/maple-shim.c
> +++ b/tools/testing/shared/maple-shim.c
> @@ -6,3 +6,9 @@
>  #include <linux/slab.h>
>
>  #include "../../../lib/maple_tree.c"
> +
> +void maple_rcu_cb(struct rcu_head *head) {
> +       struct maple_node *node = container_of(head, struct maple_node, rcu);
> +
> +       kmem_cache_free(maple_node_cache, node);
> +}
>
> --
> 2.51.0
>