linux-kernel - Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu

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Message-ID: <1b4afd82-83cb-0060-7cab-8e16d2e69ff9@linaro.org>
Date:   Tue, 14 Feb 2023 08:55:32 +0100
From:   Philippe Mathieu-Daudé <philmd@...aro.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>, linux-kernel@...r.kernel.org
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Subject: Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

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@...nel.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 */