Re: [PATCH v2] ARM: Don't use complete() during __cpu_die

[Mark Rutland]

Hi Russell,

On Thu, Feb 05, 2015 at 10:50:35AM +0000, Russell King - ARM Linux wrote:
> On Thu, Feb 05, 2015 at 11:14:30AM +0100, Krzysztof Kozlowski wrote:
> > The complete() should not be used on offlined CPU. Rewrite the
> > wait-complete mechanism with wait_on_bit_timeout().
> 
> Yuck.
> 
> I think that the IPI idea would be far better, and a much smaller patch.
> We can continue using the completions, but instead of running the
> completion on the dying CPU, the dying CPU triggers an IPI which does
> the completion on the requesting CPU.

This does look _much_ nicer than the bitmask approach.

[...]

> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 194df2f1aa87..c623e27a9c85 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -73,6 +73,9 @@ enum ipi_msg_type {
>  	IPI_IRQ_WORK,
>  	IPI_COMPLETION,
>  	IPI_CPU_BACKTRACE,
> +#ifdef CONFIG_HOTPLUG_CPU
> +	IPI_CPU_DEAD,
> +#endif
>  };

[...]

>  static const char *ipi_types[NR_IPI] __tracepoint_string = {
>  #define S(x,s)	[x] = s
>  	S(IPI_WAKEUP, "CPU wakeup interrupts"),

We'll probably want to add an entry here ("CPU teardown interrupts"?),
and bump NR_IPI in asm/hardirq.h.

Thanks,
Mark.
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