[PATCH 21/22] ARM: CPU hotplug: ensure correct ordering of unplug

[Catalin Marinas]

On 3 December 2010 20:26, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> Don't call idle_task_exit() with interrupts disabled, and ensure
> that we have a memory barrier after interrupts are disabled but
> before signalling that this CPU has shut down.
>
> Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> ---
>  arch/arm/kernel/smp.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index bebe3bd..8cc9c03 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -269,9 +269,11 @@ void __ref cpu_die(void)
>  {
>        unsigned int cpu = smp_processor_id();
>
> -       local_irq_disable();
>        idle_task_exit();
>
> +       local_irq_disable();
> +       mb();
> +
>        /* Tell __cpu_die() that this CPU is now safe to dispose of */
>        complete(&cpu_died);

I don't fully understand the point of the mb() here. If you want to
drain the write buffer that would be a dsb().

-- 
Catalin