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

Philippe Mathieu-Daudé
2023-02-14T07:56:15Z

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@kernel.org>
> ---
> 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 */