diff mbox series

[v2,04/24] arm64/cpu: Mark cpu_die() __noreturn

Message ID e47fc487980d5330e6059ac6e16416bec88cda0e.1676358308.git.jpoimboe@kernel.org
State New
Headers show
Series cpu,sched: Mark arch_cpu_idle_dead() __noreturn | expand

Commit Message

Josh Poimboeuf Feb. 14, 2023, 7:05 a.m. UTC
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@kernel.org>
---
 arch/arm64/include/asm/smp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Philippe Mathieu-Daudé Feb. 14, 2023, 8:13 a.m. UTC | #1
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@kernel.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?
Mark Rutland Feb. 15, 2023, 1:09 p.m. UTC | #2
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@kernel.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.

With that fixup:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

---->8----
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index ffc5d76cf695..a98a76f7c1c6 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -361,7 +361,7 @@ void __cpu_die(unsigned int cpu)
  * Called from the idle thread for the CPU which has been shutdown.
  *
  */
-void cpu_die(void)
+void __noreturn cpu_die(void)
 {
        unsigned int cpu = smp_processor_id();
        const struct cpu_operations *ops = get_cpu_ops(cpu);
Josh Poimboeuf Feb. 15, 2023, 7:45 p.m. UTC | #3
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@kernel.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@arm.com>

Thanks!
diff mbox series

Patch

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);
 
 static inline void cpu_park_loop(void)