linux-kernel - Re: [PATCH v2 17/24] x86/cpu: Make sure play

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Message-ID: <579b0715-dba2-246c-63a1-7e0ef4e9f9a5@linaro.org>
Date:   Tue, 14 Feb 2023 09:05:07 +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 17/24] x86/cpu: Make sure play_dead() doesn't return

On 14/2/23 08:05, Josh Poimboeuf wrote:
> After commit 076cbf5d2163 ("x86/xen: don't let xen_pv_play_dead()
> return"), play_dead() never returns.  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/x86/include/asm/smp.h | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index b4dbb20dab1a..8f628e08b25a 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -96,6 +96,7 @@ static inline void __cpu_die(unsigned int cpu)
>   static inline void play_dead(void)
>   {
>   	smp_ops.play_dead();
> +	BUG();
>   }

Similarly, smp_ops::play_dead() should be decorated noreturn first.