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Subject: Re: [PATCH v2 1/2] cpu/hotplug: Fix build error of using
 {add,remove}_cpu() with !CONFIG_SMP
To:     shuo.a.liu@intel.com, linux-next@vger.kernel.org
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Qais Yousef <qais.yousef@arm.com>, linux-kernel@vger.kernel.org
References: <20210212165519.82126-1-shuo.a.liu@intel.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <e3095871-ac55-baba-8712-9afaa94b41f8@infradead.org>
Date:   Fri, 12 Feb 2021 12:33:08 -0800
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On 2/12/21 8:55 AM, shuo.a.liu@intel.com wrote:
> From: Shuo Liu <shuo.a.liu@intel.com>
> 
> 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to
> control vCPU") introduced {add,remove}_cpu() usage and it hit below
> error with !CONFIG_SMP:
> 
> ../drivers/virt/acrn/hsm.c: In function ‘remove_cpu_store’:
> ../drivers/virt/acrn/hsm.c:389:3: error: implicit declaration of function ‘remove_cpu’; [-Werror=implicit-function-declaration]
>    remove_cpu(cpu);
> 
> ../drivers/virt/acrn/hsm.c:402:2: error: implicit declaration of function ‘add_cpu’; [-Werror=implicit-function-declaration]
>    add_cpu(cpu);
> 
> Add add_cpu() function prototypes with !CONFIG_SMP and remove_cpu() with
> !CONFIG_HOTPLUG_CPU for such usage.
> 
> Fixes: 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to control vCPU")
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
> ---
> I followed Greg's idea that add {add,remove}_cpu() functions prototypes.
> The v2 solution is different from the v1, so i removed Randy's Acked-by.
> Randy, please help have a look on v2.
> 
> v2:
>   - Drop the #ifdef in .c solution. Add {add,remove}_cpu() prototypes. (Suggested by Greg)
> 
>  include/linux/cpu.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 3aaa0687e8df..94a578a96202 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -108,6 +108,8 @@ static inline void cpu_maps_update_done(void)
>  {
>  }
>  
> +static inline int add_cpu(unsigned int cpu) { return 0;}
> +
>  #endif /* CONFIG_SMP */
>  extern struct bus_type cpu_subsys;
>  
> @@ -137,6 +139,7 @@ static inline int  cpus_read_trylock(void) { return true; }
>  static inline void lockdep_assert_cpus_held(void) { }
>  static inline void cpu_hotplug_disable(void) { }
>  static inline void cpu_hotplug_enable(void) { }
> +static inline int remove_cpu(unsigned int cpu) { return -EPERM; }

I would have done: return 0;

Anyway:

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested


>  static inline void smp_shutdown_nonboot_cpus(unsigned int primary_cpu) { }
>  #endif	/* !CONFIG_HOTPLUG_CPU */

thanks.

-- 
~Randy