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Date: Tue, 3 Apr 2018 10:13:26 +1000
From: Balbir Singh <bsingharora@gmail.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org, Vasant Hegde
 <hegdevasant@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 1/3] powerpc: use NMI IPI for smp_send_stop
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On Sun,  1 Apr 2018 20:36:13 +1000
Nicholas Piggin <npiggin@gmail.com> wrote:

> Use the NMI IPI rather than smp_call_function for smp_send_stop.
> Have stopped CPUs hard disable interrupts rather than just soft
> disable.
> 
> This function is used in crash/panic/shutdown paths to bring other
> CPUs down as quickly and reliably as possible, and minimizing their
> potential to cause trouble.
> 
> Avoiding the Linux smp_call_function infrastructure and (if supported)
> using true NMI IPIs makes this more robust.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kernel/smp.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index cfc08b099c49..db88660bf6bd 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -565,7 +565,11 @@ void crash_send_ipi(void (*crash_ipi_callback)(struct pt_regs *))
>  }
>  #endif
>  
> +#ifdef CONFIG_NMI_IPI
> +static void stop_this_cpu(struct pt_regs *regs)
> +#else
>  static void stop_this_cpu(void *dummy)
> +#endif
>  {
>  	/* Remove this CPU */
>  	set_cpu_online(smp_processor_id(), false);
> @@ -577,7 +581,11 @@ static void stop_this_cpu(void *dummy)
>  
>  void smp_send_stop(void)
>  {
> +#ifdef CONFIG_NMI_IPI
> +	smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, stop_this_cpu, 1000000);

I wonder if the delay_us should be a function of number of cpus and the
callee should figure this out on its own? May be not in this series, but
in the longer run.


Balbir Singh.