linux-kernel - Re: [PATCH v2 13/24] sh/cpu: Make sure play

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Message-ID: <20230214182831.7l73rzoeqjowbyly@treble>
Date:   Tue, 14 Feb 2023 10:28:31 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Philippe Mathieu-Daudé <philmd@...aro.org>
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Subject: Re: [PATCH v2 13/24] sh/cpu: Make sure play_dead() doesn't return

On Tue, Feb 14, 2023 at 08:57:39AM +0100, Philippe Mathieu-Daudé wrote:
> On 14/2/23 08:05, Josh Poimboeuf wrote:
> > play_dead() 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/sh/include/asm/smp-ops.h | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/sh/include/asm/smp-ops.h b/arch/sh/include/asm/smp-ops.h
> > index e27702130eb6..63866b1595a0 100644
> > --- a/arch/sh/include/asm/smp-ops.h
> > +++ b/arch/sh/include/asm/smp-ops.h
> > @@ -27,6 +27,7 @@ static inline void plat_smp_setup(void)
> >   static inline void play_dead(void)
> >   {
> >   	mp_ops->play_dead();
> > +	BUG();
> >   }
> 
> Shouldn't we decorate plat_smp_ops::play_dead() as noreturn first?

I guess it really depends on how far we want to go down the __noreturn
rabbit hole.  To keep the patch set constrained yet still useful I
stopped when I got to a function pointer, as I think it still needs a
BUG() afterwards either way.

That said, there would still be benefits of adding __noreturn to
function pointers, I just wanted to keep the patch set down to a
manageable size ;-)

-- 
Josh