linux-kernel - Re: [PATCH mptcp-next] static_call: fix unused variable warn w/o MODULE

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Date:   Fri, 26 Mar 2021 12:12:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Matthieu Baerts <matthieu.baerts@...sares.net>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH mptcp-next] static_call: fix unused variable warn w/o
 MODULE

On Fri, Mar 26, 2021 at 11:50:23AM +0100, Matthieu Baerts wrote:
> Here is the warning converted as error and reported by GCC:
> 
>   kernel/static_call.c: In function ‘__static_call_update’:
>   kernel/static_call.c:153:18: error: unused variable ‘mod’ [-Werror=unused-variable]
>     153 |   struct module *mod = site_mod->mod;
>         |                  ^~~
>   cc1: all warnings being treated as errors
>   make[1]: *** [scripts/Makefile.build:271: kernel/static_call.o] Error 1
> 
> This is simply because since recently, we no longer use 'mod' variable
> elsewhere if MODULE is unset.
> 
> When using 'make tinyconfig' to generate the default kconfig, MODULE is
> unset.
> 
> There are different ways to fix this warning. Here I tried to minimised
> the number of modified lines and not add more #ifdef. We could also move
> the declaration of the 'mod' variable inside the if-statement or
> directly use site_mod->mod.
> 
> Fixes: 698bacefe993 ("static_call: Align static_call_is_init() patching condition")
> Signed-off-by: Matthieu Baerts <matthieu.baerts@...sares.net>
> ---
> 
> Notes:
>     Feel free to modify this patch directly if you prefer. I can of course
>     send a new version if needed.

Ah, I had indeed meant to take a look at this, but hadn't come around to
it. I think this is as nice a solution as there is, so let me go apply
this.

>  kernel/static_call.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/static_call.c b/kernel/static_call.c
> index 2c5950b0b90e..723fcc9d20db 100644
> --- a/kernel/static_call.c
> +++ b/kernel/static_call.c
> @@ -165,13 +165,13 @@ void __static_call_update(struct static_call_key *key, void *tramp, void *func)
>  
>  		stop = __stop_static_call_sites;
>  
> -#ifdef CONFIG_MODULES
>  		if (mod) {
> +#ifdef CONFIG_MODULES
>  			stop = mod->static_call_sites +
>  			       mod->num_static_call_sites;
>  			init = mod->state == MODULE_STATE_COMING;
> -		}
>  #endif
> +		}
>