linux-kernel - Re: [PATCH 1/2] module: Override -EEXISTS module return

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Message-ID: <17dae27f-12c6-4a7b-b315-f7404abeae70@kernel.org>
Date: Sun, 16 Nov 2025 21:46:26 +0100
From: Daniel Gomez <da.gomez@...nel.org>
To: Lucas De Marchi <lucas.demarchi@...el.com>,
 linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Petr Pavlu <petr.pavlu@...e.com>
Subject: Re: [PATCH 1/2] module: Override -EEXISTS module return

On 13/10/2025 18.26, Lucas De Marchi wrote:
> The -EEXIST errno is reserved by the module loading functionality. When
> userspace calls [f]init_module(), it expects a -EEXIST to mean that the
> module is already loaded in the kernel. If module_init() returns it,
> that is not true anymore.
> 
> Add a warning and override the return code to workaround modules
> currently returning the wrong code. It's expected that they eventually
> migrate to a better suited error.
> 
> Closes: https://lore.kernel.org/all/aKLzsAX14ybEjHfJ@orbyte.nwl.cc/

Technically not true anymore since I delayed this review for quite some time.

FYI, this other patch actually fixes the problem for that driver:

54416fd76770 netfilter: conntrack: helper: Replace -EEXIST by -EBUSY

> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
> ---
>  kernel/module/main.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index c66b261849362..74ff87b13c517 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -3038,6 +3038,11 @@ static noinline int do_init_module(struct module *mod)
>  	if (mod->init != NULL)
>  		ret = do_one_initcall(mod->init);
>  	if (ret < 0) {
> +		if (ret == -EEXIST) {
> +			pr_warn("%s: init suspiciously returned -EEXIST: Overriding with -EBUSY\n",
> +				mod->name);
> +			ret = -EBUSY;
> +		}
>  		goto fail_free_freeinit;
>  	}
>  	if (ret > 0) {
>