Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 2 Mar 2022 10:14:00 +0100 (CET)
From:   Miroslav Benes <mbenes@suse.cz>
To:     cgel.zte@gmail.com
cc:     mcgrof@kernel.org, linux-modules@vger.kernel.org,
        linux-kernel@vger.kernel.org, Lv Ruyi <lv.ruyi@zte.com.cn>,
        Zeal Robot <zealci@zte.com.cn>
Subject: Re: [PATCH] module: avoid calling synchronize_rcu()
In-Reply-To: <20220302011306.2054550-1-lv.ruyi@zte.com.cn>
Message-ID: <alpine.LSU.2.21.2203021012250.5895@pobox.suse.cz>
References: <20220302011306.2054550-1-lv.ruyi@zte.com.cn>
User-Agent: Alpine 2.21 (LSU 202 2017-01-01)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

Hi,

On Wed, 2 Mar 2022, cgel.zte@gmail.com wrote:

> From: Lv Ruyi (CGEL ZTE) <lv.ruyi@zte.com.cn>
> 
> Kfree_rcu() usually results in even simpler code than does 
> synchronize_rcu() without synchronize_rcu()'s multi-millisecond
> latency, so replace synchronize_rcu() with kfree_rcu().
> 
> Reported-by: Zeal Robot <zealci@zte.com.cn>
> Signed-off-by: Lv Ruyi (CGEL ZTE) <lv.ruyi@zte.com.cn>
> ---
>  kernel/module.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 6cea788fd965..767b5f9e5819 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -4138,8 +4138,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
>   ddebug_cleanup:
>  	ftrace_release_mod(mod);
>  	dynamic_debug_remove(mod, info->debug);
> -	synchronize_rcu();
> -	kfree(mod->args);
> +	kfree_rcu(mod->args);

this has been proposed already. synchronize_rcu() and kfree() here are not 
really tied together. See the discussion at 
https://lore.kernel.org/all/alpine.LSU.2.21.2111301132220.3922@pobox.suse.cz/T/#u

Regards
Miroslav