Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Philippe Mathieu-Daudé]

Hi Josh,

On 14/2/23 08:05, Josh Poimboeuf wrote:
> cpu_die() doesn't return.  Make that more explicit with a BUG().
>
> BUG() is preferable to unreachable() because BUG() is a more explicit
> failure mode and avoids undefined behavior like falling off the edge of
> the function into whatever code happens to be next.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
>   arch/xtensa/kernel/smp.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
> index 4dc109dd6214..7bad78495536 100644
> --- a/arch/xtensa/kernel/smp.c
> +++ b/arch/xtensa/kernel/smp.c

Can you update the documentation along? Currently we have:

  /*
   * Called from the idle thread for the CPU which has been shutdown.
   *
   * Note that we disable IRQs here, but do not re-enable them
   * before returning to the caller. This is also the behaviour
   * of the other hotplug-cpu capable cores, so presumably coming
   * out of idle fixes this.
   */

> @@ -341,6 +341,8 @@ void __ref cpu_die(void)
>   	__asm__ __volatile__(
>   			"	movi	a2, cpu_restart\n"
>   			"	jx	a2\n");
> +
> +	BUG();
>   }
>   
>   #endif /* CONFIG_HOTPLUG_CPU */