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Date:   Wed, 11 Oct 2023 12:20:07 -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 v2] module: Add CONFIG_MODULE_LOAD_IN_SEQUENCE option
Message-ID: <ZSb1Z6EcogoUYcOR@bombadil.infradead.org>
References: <20231011074438.6098-1-quic_jiangenj@quicinc.com>
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Sender: Luis Chamberlain <mcgrof@infradead.org>
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On Wed, Oct 11, 2023 at 01:14:38PM +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  |  3 ++-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> 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..e238a31d09eb 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -2594,7 +2594,8 @@ static noinline int do_init_module(struct module *mod)
>  	 * rcu_barrier()
>  	 */
>  	if (llist_add(&freeinit->node, &init_free_list))
> -		schedule_work(&init_free_wq);
> +		if (!IS_ENABLED(CONFIG_MODULE_LOAD_IN_SEQUENCE)) {
> +			schedule_work(&init_free_wq);
>  

As Christoph suggested the rationale for something like this needs to be
clearly spelled out in the commit log and if so valuable it should be
a default. The commit log and even the Kconfig description do little
to justify any rationale for this.

  Luis