linux-kernel - Re: [PATCH] maple_tree: Remove redundant mte_to_node() in mte_dead

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <j7vbmbqwapzfs4vnkb6jfbprmdwzzq6fu7jjpvcb3q5szdvh7s@p7p5ur2ivlts>
Date: Mon, 10 Feb 2025 09:51:42 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: I Hsin Cheng <richard120310@...il.com>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        jserv@...s.ncku.edu.tw, skhan@...uxfoundation.org
Subject: Re: [PATCH] maple_tree: Remove redundant mte_to_node() in
 mte_dead_node()

* I Hsin Cheng <richard120310@...il.com> [250210 03:35]:

> In mte_dead_node(), it already assign "node" as "mte_to_node(enode)" in
> the first place, calling "mte_parent(enode)" will result in the same
> "mte_to_node(enode)" again which is redundant.

This is a very confusing way of saying "avoid calling mte_to_node() in
the mte_parent() call by using the ma_dead_node() instead."

In fact, the subject is wrong as well, since the mte_to_node() was
removed from the call path of mte_dead_node(), and not the function
itself.

> 
> Refactor mte_dead_node() and utilize ma_dead_node() to perform the
> parent check without the redundant "mte_to_node()".
> 
> Signed-off-by: I Hsin Cheng <richard120310@...il.com>

The code looks right, but the subject and change log are not.  Please
respin the patch, something like this:

maple_tree: Use ma_dead_node() in mte_dead_node()

Using ma_dead_node() in mte_dead_node() avoids decoding the maple enode
for a second time to find the parent.

Feel free to change it as you'd like, but I couldn't follow what you
meant.

> ---
>  lib/maple_tree.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index f7153ade1be5..362f85c62678 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -584,13 +584,10 @@ static __always_inline bool ma_dead_node(const struct maple_node *node)
>   */
>  static __always_inline bool mte_dead_node(const struct maple_enode *enode)
>  {
> -	struct maple_node *parent, *node;
> +	struct maple_node *node;
>  
>  	node = mte_to_node(enode);
> -	/* Do not reorder reads from the node prior to the parent check */
> -	smp_rmb();
> -	parent = mte_parent(enode);
> -	return (parent == node);
> +	return ma_dead_node(node);
>  }
>  
>  /*
> -- 
> 2.43.0
>