linux-kernel - Re: [PATCH] rcu: remove unused variable in boot_cpu_state

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Date:   Wed, 21 Jun 2017 15:10:54 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: remove unused variable in boot_cpu_state_init

On Wed, Jun 21, 2017 at 11:57:28PM +0200, Arnd Bergmann wrote:
> Without CONFIG_SMP, we get a harmless warning about
> an unused variable:
> 
> kernel/cpu.c: In function 'boot_cpu_state_init':
> kernel/cpu.c:1778:6: error: unused variable 'cpu' [-Werror=unused-variable]
> 
> This reworks the function to have the declaration inside
> of the #ifdef.
> 
> Fixes: faeb334286b7 ("rcu: Migrate callbacks earlier in the CPU-offline timeline")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

I simply added a __maybe_unused in 6441c656acde ("rcu: Migrate callbacks
earlier in the CPU-offline timeline") in my -rcu tree.  However, your
approach does have the advantage of complaining if the code using that
variable is removed.

So, would you be OK with my folding your approach into my commit with
attribution?

							Thanx, Paul

> ---
>  kernel/cpu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index f13ad79e785d..9cd4fc35a66f 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1775,11 +1775,11 @@ void __init boot_cpu_init(void)
>   */
>  void __init boot_cpu_state_init(void)
>  {
> +#ifdef CONFIG_SMP
>  	int cpu;
> 
> -	per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE;
> -#ifdef CONFIG_SMP
>  	for_each_possible_cpu(cpu)
>  		per_cpu_ptr(&cpuhp_state, cpu)->cpu = cpu;
>  #endif
> +	per_cpu_ptr(&cpuhp_state, smp_processor_id())->state = CPUHP_ONLINE;
>  }
> -- 
> 2.9.0
>