Re: [PATCH v4 01/17] cpu: Add new {add,remove}_cpu() functions

[Paul E. McKenney]

On Mon, Mar 23, 2020 at 01:50:54PM +0000, Qais Yousef wrote:
> The new functions use device_{online,offline}() which are userspace
> safe.
> 
> This is in preparation to move cpu_{up, down} kernel users to use
> a safer interface that is not racy with userspace.
> 
> Suggested-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

> CC: Helge Deller <deller@xxxxxx>
> CC: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
> CC: Mark Rutland <mark.rutland@xxxxxxx>
> CC: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> CC: xen-devel@xxxxxxxxxxxxxxxxxxxx
> CC: linux-parisc@xxxxxxxxxxxxxxx
> CC: sparclinux@xxxxxxxxxxxxxxx
> CC: linuxppc-dev@xxxxxxxxxxxxxxxx
> CC: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> CC: x86@xxxxxxxxxx
> CC: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  include/linux/cpu.h |  2 ++
>  kernel/cpu.c        | 24 ++++++++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 1ca2baf817ed..cf8cf38dca43 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -89,6 +89,7 @@ extern ssize_t arch_cpu_release(const char *, size_t);
>  #ifdef CONFIG_SMP
>  extern bool cpuhp_tasks_frozen;
>  int cpu_up(unsigned int cpu);
> +int add_cpu(unsigned int cpu);
>  void notify_cpu_starting(unsigned int cpu);
>  extern void cpu_maps_update_begin(void);
>  extern void cpu_maps_update_done(void);
> @@ -118,6 +119,7 @@ extern void cpu_hotplug_disable(void);
>  extern void cpu_hotplug_enable(void);
>  void clear_tasks_mm_cpumask(int cpu);
>  int cpu_down(unsigned int cpu);
> +int remove_cpu(unsigned int cpu);
>  
>  #else /* CONFIG_HOTPLUG_CPU */
>  
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 9c706af713fb..069802f7010f 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1057,6 +1057,18 @@ int cpu_down(unsigned int cpu)
>  }
>  EXPORT_SYMBOL(cpu_down);
>  
> +int remove_cpu(unsigned int cpu)
> +{
> +	int ret;
> +
> +	lock_device_hotplug();
> +	ret = device_offline(get_cpu_device(cpu));
> +	unlock_device_hotplug();
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(remove_cpu);
> +
>  #else
>  #define takedown_cpu		NULL
>  #endif /*CONFIG_HOTPLUG_CPU*/
> @@ -1209,6 +1221,18 @@ int cpu_up(unsigned int cpu)
>  }
>  EXPORT_SYMBOL_GPL(cpu_up);
>  
> +int add_cpu(unsigned int cpu)
> +{
> +	int ret;
> +
> +	lock_device_hotplug();
> +	ret = device_online(get_cpu_device(cpu));
> +	unlock_device_hotplug();
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(add_cpu);
> +
>  #ifdef CONFIG_PM_SLEEP_SMP
>  static cpumask_var_t frozen_cpus;
>  
> -- 
> 2.17.1
>