linux-kernel - Re: [PATCH] smp_call_function: use inline helpers instead of macros

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Date:   Thu, 11 May 2017 17:34:19 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] smp_call_function: use inline helpers instead of macros



On 11/05/2017 17:13, Arnd Bergmann wrote:
> A new caller of smp_call_function() passes a local variable as the 'wait'
> argument, and that variable is otherwise unused, so we get a warning
> in non-SMP configurations:
> 
> virt/kvm/kvm_main.c: In function 'kvm_make_all_cpus_request':
> virt/kvm/kvm_main.c:195:7: error: unused variable 'wait' [-Werror=unused-variable]
>   bool wait = req & KVM_REQUEST_WAIT;
> 
> This addresses the warning by changing the two macros into inline functions.
> 
> Fixes: 7a97cec26b94 ("KVM: mark requests that need synchronization")
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/smp.h | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index e978ec742103..acd401c0c77d 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -144,13 +144,20 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info)
>  {
>  	return 0;
>  }
> -#define smp_call_function(func, info, wait) \
> -			(up_smp_call_function(func, info))
> +static inline int smp_call_function(smp_call_func_t func, void *info, int wait)
> +{
> +	return up_smp_call_function(func, info);
> +}

You can just delete up_smp_call_function and return 0.  The purpose of
up_smp_call_function was only to eat warnings about those two arguments,
as far as I could see.

(I sent almost exactly the same patch to Paul this morning).

Paolo

>  
>  static inline void smp_send_reschedule(int cpu) { }
>  #define smp_prepare_boot_cpu()			do {} while (0)
> -#define smp_call_function_many(mask, func, info, wait) \
> -			(up_smp_call_function(func, info))
> +
> +static inline void smp_call_function_many(const struct cpumask *mask,
> +			    smp_call_func_t func, void *info, bool wait)
> +{
> +	up_smp_call_function(func, info);
> +}
> +
>  static inline void call_function_init(void) { }
>  
>  static inline int
>