RE: [PATCH 1/1] cpu-hotplug: export cpu_hotplug_enable/cpu_hotplug_disable

[KY Srinivasan]

> -----Original Message-----
> From: K. Y. Srinivasan [mailto:kys@xxxxxxxxxxxxx]
> Sent: Sunday, June 21, 2015 7:56 PM
> To: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; mingo@xxxxxxxxxx; peterz@xxxxxxxxxxxxx;
> rafael.j.wysocki@xxxxxxxxx; tglx@xxxxxxxxxxxxx
> Cc: Vitaly Kuznetsov; KY Srinivasan
> Subject: [PATCH 1/1] cpu-hotplug: export
> cpu_hotplug_enable/cpu_hotplug_disable
> 
> From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> 
> Loaded Hyper-V module will use these functions to disable CPU
> hotplug under certain circumstances. Convert cpu_hotplug_disabled
> to a counter (protected by cpu_add_remove_lock) to support e.g.
> disable -> disable -> enable call sequences.

Greg is willing to take this patch through his tree if gets an ack. Please provide your feedback.

Regards,

K. Y
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> ---
>  Documentation/power/suspend-and-cpuhotplug.txt |    6 +++---
>  kernel/cpu.c                                   |   13 ++++++++-----
>  2 files changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/power/suspend-and-cpuhotplug.txt
> b/Documentation/power/suspend-and-cpuhotplug.txt
> index 2850df3..2fc9095 100644
> --- a/Documentation/power/suspend-and-cpuhotplug.txt
> +++ b/Documentation/power/suspend-and-cpuhotplug.txt
> @@ -72,7 +72,7 @@ More details follow:
>                                          |
>                                          v
>                             Disable regular cpu hotplug
> -                        by setting cpu_hotplug_disabled=1
> +                        by increasing cpu_hotplug_disabled
>                                          |
>                                          v
>                              Release cpu_add_remove_lock
> @@ -89,7 +89,7 @@ Resuming back is likewise, with the counterparts being
> (in the order of
>  execution during resume):
>  * enable_nonboot_cpus() which involves:
>     |  Acquire cpu_add_remove_lock
> -   |  Reset cpu_hotplug_disabled to 0, thereby enabling regular cpu hotplug
> +   |  Decrease cpu_hotplug_disabled, thereby enabling regular cpu hotplug
>     |  Call _cpu_up() [for all those cpus in the frozen_cpus mask, in a loop]
>     |  Release cpu_add_remove_lock
>     v
> @@ -120,7 +120,7 @@ after the entire cycle is complete (i.e., suspend +
> resume).
>                             Acquire cpu_add_remove_lock
>                                          |
>                                          v
> -                          If cpu_hotplug_disabled is 1
> +                          If cpu_hotplug_disabled > 0
>                                  return gracefully
>                                          |
>                                          |
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 94bbe46..8f35ee6 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -190,17 +190,19 @@ void cpu_hotplug_done(void)
>  void cpu_hotplug_disable(void)
>  {
>  	cpu_maps_update_begin();
> -	cpu_hotplug_disabled = 1;
> +	cpu_hotplug_disabled++;
>  	cpu_maps_update_done();
>  }
> +EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
> 
>  void cpu_hotplug_enable(void)
>  {
>  	cpu_maps_update_begin();
> -	cpu_hotplug_disabled = 0;
> +	if (cpu_hotplug_disabled)
> +		cpu_hotplug_disabled--;
>  	cpu_maps_update_done();
>  }
> -
> +EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
>  #endif	/* CONFIG_HOTPLUG_CPU */
> 
>  /* Need to know about CPUs going up/down? */
> @@ -600,7 +602,7 @@ int disable_nonboot_cpus(void)
>  	if (!error) {
>  		BUG_ON(num_online_cpus() > 1);
>  		/* Make sure the CPUs won't be enabled by someone else
> */
> -		cpu_hotplug_disabled = 1;
> +		cpu_hotplug_disabled++;
>  	} else {
>  		pr_err("Non-boot CPUs are not disabled\n");
>  	}
> @@ -622,7 +624,8 @@ void __ref enable_nonboot_cpus(void)
> 
>  	/* Allow everyone to use the CPU hotplug again */
>  	cpu_maps_update_begin();
> -	cpu_hotplug_disabled = 0;
> +	if (cpu_hotplug_disabled)
> +		cpu_hotplug_disabled--;
>  	if (cpumask_empty(frozen_cpus))
>  		goto out;
> 
> --
> 1.7.4.1

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