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Date:   Tue, 10 Oct 2023 15:36:28 -0700
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Joey Jiao <quic_jiangenj@quicinc.com>
Cc:     linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] module: Add CONFIG_MODULE_LOAD_IN_SEQUENCE option
Message-ID: <ZSXR7PJmXZpZxQ2R@bombadil.infradead.org>
References: <20231009045636.4143-1-quic_jiangenj@quicinc.com>
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Sender: Luis Chamberlain <mcgrof@infradead.org>
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On Mon, Oct 09, 2023 at 10:26:35AM +0530, Joey Jiao wrote:
> When modprobe cmds are executed one by one, the final loaded modules
> are not in fixed sequence as expected.
> 
> Add the option to make sure modules are in fixed sequence across reboot.
> 
> Signed-off-by: Joey Jiao <quic_jiangenj@quicinc.com>
> ---
>  kernel/module/Kconfig | 11 +++++++++++
>  kernel/module/main.c  |  6 ++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> index 33a2e991f608..b45a45f31d6d 100644
> --- a/kernel/module/Kconfig
> +++ b/kernel/module/Kconfig
> @@ -389,4 +389,15 @@ config MODULES_TREE_LOOKUP
>  	def_bool y
>  	depends on PERF_EVENTS || TRACING || CFI_CLANG
>  
> +config MODULE_LOAD_IN_SEQUENCE
> +	bool "Load module in sequence"
> +	default n
> +	help
> +	  By default, modules are loaded in random sequence depending on when modprobe
> +	  is executed.
> +
> +	  This option allows modules to be loaded in sequence if modprobe cmds are
> +	  executed one by one in sequence. This option is helpful during syzkaller fuzzing
> +	  to make sure module is loaded into fixed address across device reboot.
> +
>  endif # MODULES
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 98fedfdb8db5..587fd84083ae 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -2593,11 +2593,17 @@ static noinline int do_init_module(struct module *mod)
>  	 * be cleaned up needs to sync with the queued work - ie
>  	 * rcu_barrier()
>  	 */
> +#ifdef CONFIG_MODULE_LOAD_IN_SEQUENCE
> +	llist_add(&freeinit->node, &init_free_list);
> +#else
>  	if (llist_add(&freeinit->node, &init_free_list))
>  		schedule_work(&init_free_wq);
> +#endif

How is ignoring an error ensuring ordering?

>  	mutex_unlock(&module_mutex);
> +#ifdef CONFIG_MODULE_LOAD_IN_SEQUENCE
>  	wake_up_all(&module_wq);
> +#endif

Why are you making this only now be called with this new kconfig option?

  Luis