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);
 
 static inline void cpu_park_loop(void)
-- 
2.39.1

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?

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);

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!

-- 
Josh

cpu_die() doesn't return.  Annotate it as such.  By extension this also
makes arch_cpu_idle_dead() noreturn.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/arm64/include/asm/smp.h | 2 +-
 arch/arm64/kernel/smp.c      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

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)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 4e8327264255..d5d09a18b4f8 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);
-- 
2.39.1

On 16/2/23 19:41, Josh Poimboeuf wrote:
> cpu_die() doesn't return.  Annotate it as such.  By extension this also
> makes arch_cpu_idle_dead() noreturn.
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>   arch/arm64/include/asm/smp.h | 2 +-
>   arch/arm64/kernel/smp.c      | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     9bdc61ef27db5eaac48f1cc5deb8224603e79c89
Gitweb:        https://git.kernel.org/tip/9bdc61ef27db5eaac48f1cc5deb8224603e79c89
Author:        Josh Poimboeuf <jpoimboe@kernel.org>
AuthorDate:    Thu, 16 Feb 2023 10:42:01 -08:00
Committer:     Josh Poimboeuf <jpoimboe@kernel.org>
CommitterDate: Mon, 06 Mar 2023 15:34:04 -08:00

arm64/cpu: Mark cpu_die() __noreturn

cpu_die() doesn't return.  Annotate it as such.  By extension this also
makes arch_cpu_idle_dead() noreturn.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lkml.kernel.org/r/20230216184157.4hup6y6mmspr2kll@treble
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/arm64/include/asm/smp.h | 2 +-
 arch/arm64/kernel/smp.c      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index fc55f5a..5733a31 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)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 4e83272..d5d09a1 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);