linux-kernel - Re: [PATCH v2 04/24] arm64/cpu: Mark cpu_die() _

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Date:   Wed, 15 Feb 2023 11:45:38 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Philippe Mathieu-Daudé <philmd@...aro.org>,
        juri.lelli@...hat.com, dalias@...c.org, linux-ia64@...r.kernel.org,
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Subject: Re: [PATCH v2 04/24] arm64/cpu: Mark cpu_die() __noreturn

On Wed, Feb 15, 2023 at 01:09:21PM +0000, Mark Rutland wrote:
> On Tue, Feb 14, 2023 at 09:13:08AM +0100, Philippe Mathieu-Daudé wrote:
> > On 14/2/23 08:05, Josh Poimboeuf wrote:
> > > cpu_die() doesn't return.  Annotate it as such.  By extension this also
> > > makes arch_cpu_idle_dead() noreturn.
> > > 
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> > > ---
> > >   arch/arm64/include/asm/smp.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
> > > index fc55f5a57a06..5733a31bab08 100644
> > > --- a/arch/arm64/include/asm/smp.h
> > > +++ b/arch/arm64/include/asm/smp.h
> > > @@ -100,7 +100,7 @@ static inline void arch_send_wakeup_ipi_mask(const struct cpumask *mask)
> > >   extern int __cpu_disable(void);
> > >   extern void __cpu_die(unsigned int cpu);
> > > -extern void cpu_die(void);
> > > +extern void __noreturn cpu_die(void);
> > >   extern void cpu_die_early(void);
> > 
> > Shouldn't cpu_operations::cpu_die() be declared noreturn first?
> 
> The cpu_die() function ends with a BUG(), and so does not return, even if a
> cpu_operations::cpu_die() function that it calls erroneously returned.
> 
> We *could* mark cpu_operations::cpu_die() as noreturn, but I'd prefer that we
> did not so that the compiler doesn't optimize away the BUG() which is there to
> catch such erroneous returns.
> 
> That said, could we please add __noreturn to the implementation of cpu_die() in
> arch/arm64/kernel/smp.c? i.e. the fixup below.

Done.

> With that fixup:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>

Thanks!

-- 
Josh