[PATCH v2 00/24] cpu,sched: Mark arch_cpu_idle_dead() __noreturn

[PATCH v2 00/24] cpu,sched: Mark arch_cpu_idle_dead() __noreturn

[Josh Poimboeuf]

v2:
- make arch_call_rest_init() and rest_init() __noreturn
- make objtool 'global_returns' work for weak functions
- rebase on tip/objtool/core with dependencies merged in (mingo)
- add acks

v1.1:
- add __noreturn to all arch_cpu_idle_dead() implementations (mpe)

Josh Poimboeuf (24):
  alpha/cpu: Expose arch_cpu_idle_dead()'s prototype declaration
  alpha/cpu: Make sure arch_cpu_idle_dead() doesn't return
  arm/cpu: Make sure arch_cpu_idle_dead() doesn't return
  arm64/cpu: Mark cpu_die() __noreturn
  csky/cpu: Make sure arch_cpu_idle_dead() doesn't return
  ia64/cpu: Mark play_dead() __noreturn
  loongarch/cpu: Make sure play_dead() doesn't return
  loongarch/cpu: Mark play_dead() __noreturn
  mips/cpu: Expose play_dead()'s prototype definition
  mips/cpu: Make sure play_dead() doesn't return
  mips/cpu: Mark play_dead() __noreturn
  powerpc/cpu: Mark start_secondary_resume() __noreturn
  sh/cpu: Make sure play_dead() doesn't return
  sh/cpu: Mark play_dead() __noreturn
  sh/cpu: Expose arch_cpu_idle_dead()'s prototype definition
  sparc/cpu: Mark cpu_play_dead() __noreturn
  x86/cpu: Make sure play_dead() doesn't return
  x86/cpu: Mark play_dead() __noreturn
  xtensa/cpu: Make sure cpu_die() doesn't return
  xtensa/cpu: Mark cpu_die() __noreturn
  sched/idle: Make sure weak version of arch_cpu_idle_dead() doesn't
    return
  objtool: Include weak functions in 'global_noreturns' check
  init: Make arch_call_rest_init() and rest_init() __noreturn
  sched/idle: Mark arch_cpu_idle_dead() __noreturn

 arch/alpha/kernel/process.c      |  4 +++-
 arch/arm/kernel/smp.c            |  4 +++-
 arch/arm64/include/asm/smp.h     |  2 +-
 arch/arm64/kernel/process.c      |  2 +-
 arch/csky/kernel/smp.c           |  4 +++-
 arch/ia64/kernel/process.c       |  6 +++---
 arch/loongarch/include/asm/smp.h |  2 +-
 arch/loongarch/kernel/process.c  |  2 +-
 arch/loongarch/kernel/smp.c      |  2 +-
 arch/mips/include/asm/smp.h      |  2 +-
 arch/mips/kernel/process.c       |  2 +-
 arch/mips/kernel/smp-bmips.c     |  3 +++
 arch/mips/loongson64/smp.c       |  1 +
 arch/parisc/kernel/process.c     |  2 +-
 arch/powerpc/include/asm/smp.h   |  2 +-
 arch/powerpc/kernel/smp.c        |  2 +-
 arch/riscv/kernel/cpu-hotplug.c  |  2 +-
 arch/s390/kernel/idle.c          |  2 +-
 arch/s390/kernel/setup.c         |  2 +-
 arch/sh/include/asm/smp-ops.h    |  5 +++--
 arch/sh/kernel/idle.c            |  3 ++-
 arch/sparc/include/asm/smp_64.h  |  2 +-
 arch/sparc/kernel/process_64.c   |  2 +-
 arch/x86/include/asm/smp.h       |  3 ++-
 arch/x86/kernel/process.c        |  4 ++--
 arch/xtensa/include/asm/smp.h    |  2 +-
 arch/xtensa/kernel/smp.c         |  4 +++-
 include/linux/cpu.h              |  2 +-
 include/linux/start_kernel.h     |  4 ++--
 init/main.c                      |  4 ++--
 kernel/sched/idle.c              |  2 +-
 tools/objtool/check.c            | 11 +++++++----
 32 files changed, 57 insertions(+), 39 deletions(-)

-- 
2.39.1

[PATCH v2 01/24] alpha/cpu: Expose arch_cpu_idle_dead()'s prototype declaration

[Josh Poimboeuf]

Include <linux/cpu.h> to make sure arch_cpu_idle_dead() matches its
prototype going forward.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/alpha/kernel/process.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index ce20c31828a0..d1f2e8b6b107 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -9,6 +9,7 @@
  * This file handles the architecture-dependent parts of process handling.
  */
 
+#include <linux/cpu.h>
 #include <linux/errno.h>
 #include <linux/module.h>
 #include <linux/sched.h>
-- 
2.39.1

[PATCH v2 02/24] alpha/cpu: Make sure arch_cpu_idle_dead() doesn't return

[Josh Poimboeuf]

arch_cpu_idle_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@kernel.org>
---
 arch/alpha/kernel/process.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index d1f2e8b6b107..d0ff06eda8fa 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -63,6 +63,7 @@ void arch_cpu_idle(void)
 void arch_cpu_idle_dead(void)
 {
 	wtint(INT_MAX);
+	BUG();
 }
 #endif /* ALPHA_WTINT */
 
-- 
2.39.1

[PATCH v2 03/24] arm/cpu: Make sure arch_cpu_idle_dead() doesn't return

[Josh Poimboeuf]

arch_cpu_idle_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@kernel.org>
---
 arch/arm/kernel/smp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 0b8c25763adc..adcd417c526b 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -382,6 +382,8 @@ void arch_cpu_idle_dead(void)
 		: "r" (task_stack_page(current) + THREAD_SIZE - 8),
 		  "r" (current)
 		: "r0");
+
+	BUG();
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
-- 
2.39.1

Re: [PATCH v2 03/24] arm/cpu: Make sure arch_cpu_idle_dead() doesn't return

[Russell King (Oracle)]

On Mon, Feb 13, 2023 at 11:05:37PM -0800, Josh Poimboeuf wrote:
> arch_cpu_idle_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.

This is silly. Just mark the function __noreturn and be done with it.
If the CPU ever executes code past the "b" instruction, it's already
really broken that the extra instructions that BUG() gives will be
meaningless.

This patch does nothing except add yet more bloat the kernel.

Sorry, but NAK.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

Re: [PATCH v2 03/24] arm/cpu: Make sure arch_cpu_idle_dead() doesn't return

[Josh Poimboeuf]

On Tue, Feb 14, 2023 at 11:15:23AM +0000, Russell King (Oracle) wrote:
> On Mon, Feb 13, 2023 at 11:05:37PM -0800, Josh Poimboeuf wrote:
> > arch_cpu_idle_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.
> 
> This is silly. Just mark the function __noreturn and be done with it.
> If the CPU ever executes code past the "b" instruction, it's already
> really broken that the extra instructions that BUG() gives will be
> meaningless.
> 
> This patch does nothing except add yet more bloat the kernel.
> 
> Sorry, but NAK.

Problem is, the compiler can't read inline asm.  So you'd get a 
"'noreturn' function does return" warning.

We can do an unreachable() instead of a BUG() here if you prefer
undefined behavior.

-- 
Josh

Re: [PATCH v2 03/24] arm/cpu: Make sure arch_cpu_idle_dead() doesn't return

[Russell King (Oracle)]

On Tue, Feb 14, 2023 at 10:39:26AM -0800, Josh Poimboeuf wrote:
> On Tue, Feb 14, 2023 at 11:15:23AM +0000, Russell King (Oracle) wrote:
> > On Mon, Feb 13, 2023 at 11:05:37PM -0800, Josh Poimboeuf wrote:
> > > arch_cpu_idle_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.
> > 
> > This is silly. Just mark the function __noreturn and be done with it.
> > If the CPU ever executes code past the "b" instruction, it's already
> > really broken that the extra instructions that BUG() gives will be
> > meaningless.
> > 
> > This patch does nothing except add yet more bloat the kernel.
> > 
> > Sorry, but NAK.
> 
> Problem is, the compiler can't read inline asm.  So you'd get a 
> "'noreturn' function does return" warning.
> 
> We can do an unreachable() instead of a BUG() here if you prefer
> undefined behavior.

That's fine.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

[PATCH v2.1 03/24] arm/cpu: Add unreachable() to arch_cpu_idle_dead()

[Josh Poimboeuf]

arch_cpu_idle_dead() doesn't return.  Make that visible to the compiler
with an unreachable() code annotation.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/arm/kernel/smp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 0b8c25763adc..441ea5cff390 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -382,6 +382,8 @@ void arch_cpu_idle_dead(void)
 		: "r" (task_stack_page(current) + THREAD_SIZE - 8),
 		  "r" (current)
 		: "r0");
+
+	unreachable();
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
-- 
2.39.1

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

[Josh Poimboeuf]

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

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

[Philippe Mathieu-Daudé]

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?

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

[Mark Rutland]

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);

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

[Josh Poimboeuf]

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

[PATCH v2.1 04/24] arm64/cpu: Mark cpu_die() __noreturn

[Josh Poimboeuf]

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

Re: [PATCH v2.1 04/24] arm64/cpu: Mark cpu_die() __noreturn

[Philippe Mathieu-Daudé]

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>

[PATCH v2 05/24] csky/cpu: Make sure arch_cpu_idle_dead() doesn't return

[Josh Poimboeuf]

arch_cpu_idle_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.

Acked-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/csky/kernel/smp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/csky/kernel/smp.c b/arch/csky/kernel/smp.c
index b45d1073307f..0ec20efaf5fd 100644
--- a/arch/csky/kernel/smp.c
+++ b/arch/csky/kernel/smp.c
@@ -317,5 +317,7 @@ void arch_cpu_idle_dead(void)
 		"jmpi	csky_start_secondary"
 		:
 		: "r" (secondary_stack));
+
+	BUG();
 }
 #endif
-- 
2.39.1

[PATCH v2 06/24] ia64/cpu: Mark play_dead() __noreturn

[Josh Poimboeuf]

play_dead() 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/ia64/kernel/process.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index f6195a0a00ae..78f5794b2dde 100644
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -201,7 +201,7 @@ __setup("nohalt", nohalt_setup);
 
 #ifdef CONFIG_HOTPLUG_CPU
 /* We don't actually take CPU down, just spin without interrupts. */
-static inline void play_dead(void)
+static inline void __noreturn play_dead(void)
 {
 	unsigned int this_cpu = smp_processor_id();
 
@@ -219,7 +219,7 @@ static inline void play_dead(void)
 	BUG();
 }
 #else
-static inline void play_dead(void)
+static inline void __noreturn play_dead(void)
 {
 	BUG();
 }
-- 
2.39.1

Re: [PATCH v2 06/24] ia64/cpu: Mark play_dead() __noreturn

[Philippe Mathieu-Daudé]

On 14/2/23 08:05, Josh Poimboeuf wrote:
> play_dead() 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/ia64/kernel/process.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)

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

[PATCH v2 07/24] loongarch/cpu: Make sure play_dead() doesn't return

[Josh Poimboeuf]

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@kernel.org>
---
 arch/loongarch/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
index 8c6e227cb29d..51f328169a7b 100644
--- a/arch/loongarch/kernel/smp.c
+++ b/arch/loongarch/kernel/smp.c
@@ -336,7 +336,7 @@ void play_dead(void)
 	iocsr_write32(0xffffffff, LOONGARCH_IOCSR_IPI_CLEAR);
 
 	init_fn();
-	unreachable();
+	BUG();
 }
 
 #endif
-- 
2.39.1

[PATCH v2 08/24] loongarch/cpu: Mark play_dead() __noreturn

[Josh Poimboeuf]

play_dead() 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/loongarch/include/asm/smp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
index d82687390b4a..416b653bccb4 100644
--- a/arch/loongarch/include/asm/smp.h
+++ b/arch/loongarch/include/asm/smp.h
@@ -99,7 +99,7 @@ static inline void __cpu_die(unsigned int cpu)
 	loongson_cpu_die(cpu);
 }
 
-extern void play_dead(void);
+extern void __noreturn play_dead(void);
 #endif
 
 #endif /* __ASM_SMP_H */
-- 
2.39.1

Re: [PATCH v2 08/24] loongarch/cpu: Mark play_dead() __noreturn

[Philippe Mathieu-Daudé]

On 14/2/23 08:05, Josh Poimboeuf wrote:
> play_dead() 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/loongarch/include/asm/smp.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

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

[PATCH v2 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Josh Poimboeuf]

Include <asm/smp.h> to make sure play_dead() matches its prototype going
forward.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/mips/kernel/smp-bmips.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
index f5d7bfa3472a..df9158e8329d 100644
--- a/arch/mips/kernel/smp-bmips.c
+++ b/arch/mips/kernel/smp-bmips.c
@@ -38,6 +38,7 @@
 #include <asm/traps.h>
 #include <asm/barrier.h>
 #include <asm/cpu-features.h>
+#include <asm/smp.h>
 
 static int __maybe_unused max_cpus = 1;
 
-- 
2.39.1

Re: [PATCH v2 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Philippe Mathieu-Daudé]

Hi Josh,

On 14/2/23 08:05, Josh Poimboeuf wrote:
> Include <asm/smp.h> to make sure play_dead() matches its prototype going
> forward.
> 
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>   arch/mips/kernel/smp-bmips.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
> index f5d7bfa3472a..df9158e8329d 100644
> --- a/arch/mips/kernel/smp-bmips.c
> +++ b/arch/mips/kernel/smp-bmips.c
> @@ -38,6 +38,7 @@
>   #include <asm/traps.h>
>   #include <asm/barrier.h>
>   #include <asm/cpu-features.h>
> +#include <asm/smp.h>

What about the other implementations?

$ git grep -L asm/smp.h $(git grep -wlF 'play_dead(void)' arch/mips)
arch/mips/cavium-octeon/smp.c
arch/mips/kernel/smp-bmips.c
arch/mips/kernel/smp-cps.c
arch/mips/loongson64/smp.c

Re: [PATCH v2 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Josh Poimboeuf]

On Tue, Feb 14, 2023 at 08:46:41AM +0100, Philippe Mathieu-Daudé wrote:
> Hi Josh,
> 
> On 14/2/23 08:05, Josh Poimboeuf wrote:
> > Include <asm/smp.h> to make sure play_dead() matches its prototype going
> > forward.
> > 
> > Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> > ---
> >   arch/mips/kernel/smp-bmips.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
> > index f5d7bfa3472a..df9158e8329d 100644
> > --- a/arch/mips/kernel/smp-bmips.c
> > +++ b/arch/mips/kernel/smp-bmips.c
> > @@ -38,6 +38,7 @@
> >   #include <asm/traps.h>
> >   #include <asm/barrier.h>
> >   #include <asm/cpu-features.h>
> > +#include <asm/smp.h>
> 
> What about the other implementations?
> 
> $ git grep -L asm/smp.h $(git grep -wlF 'play_dead(void)' arch/mips)
> arch/mips/cavium-octeon/smp.c
> arch/mips/kernel/smp-bmips.c
> arch/mips/kernel/smp-cps.c
> arch/mips/loongson64/smp.c

Indeed.  I really wish we had -Wmissing-prototypes.

I'll squash this in:

diff --git a/arch/mips/cavium-octeon/smp.c b/arch/mips/cavium-octeon/smp.c
index 89954f5f87fb..4212584e6efa 100644
--- a/arch/mips/cavium-octeon/smp.c
+++ b/arch/mips/cavium-octeon/smp.c
@@ -20,6 +20,7 @@
 #include <asm/mmu_context.h>
 #include <asm/time.h>
 #include <asm/setup.h>
+#include <asm/smp.h>
 
 #include <asm/octeon/octeon.h>
 
diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index bcd6a944b839..6d69a9ba8167 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -20,6 +20,7 @@
 #include <asm/mipsregs.h>
 #include <asm/pm-cps.h>
 #include <asm/r4kcache.h>
+#include <asm/smp.h>
 #include <asm/smp-cps.h>
 #include <asm/time.h>
 #include <asm/uasm.h>
diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
index c81c2bd07c62..df8d789ede3c 100644
--- a/arch/mips/loongson64/smp.c
+++ b/arch/mips/loongson64/smp.c
@@ -14,6 +14,7 @@
 #include <linux/cpufreq.h>
 #include <linux/kexec.h>
 #include <asm/processor.h>
+#include <asm/smp.h>
 #include <asm/time.h>
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>

Re: [PATCH v2 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Philippe Mathieu-Daudé]

On 14/2/23 19:11, Josh Poimboeuf wrote:
> On Tue, Feb 14, 2023 at 08:46:41AM +0100, Philippe Mathieu-Daudé wrote:
>> Hi Josh,
>>
>> On 14/2/23 08:05, Josh Poimboeuf wrote:
>>> Include <asm/smp.h> to make sure play_dead() matches its prototype going
>>> forward.
>>>
>>> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
>>> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
>>> ---
>>>    arch/mips/kernel/smp-bmips.c | 1 +
>>>    1 file changed, 1 insertion(+)
>>>
>>> diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
>>> index f5d7bfa3472a..df9158e8329d 100644
>>> --- a/arch/mips/kernel/smp-bmips.c
>>> +++ b/arch/mips/kernel/smp-bmips.c
>>> @@ -38,6 +38,7 @@
>>>    #include <asm/traps.h>
>>>    #include <asm/barrier.h>
>>>    #include <asm/cpu-features.h>
>>> +#include <asm/smp.h>
>>
>> What about the other implementations?
>>
>> $ git grep -L asm/smp.h $(git grep -wlF 'play_dead(void)' arch/mips)
>> arch/mips/cavium-octeon/smp.c
>> arch/mips/kernel/smp-bmips.c
>> arch/mips/kernel/smp-cps.c
>> arch/mips/loongson64/smp.c
> 
> Indeed.  I really wish we had -Wmissing-prototypes.
> 
> I'll squash this in:
> 
> diff --git a/arch/mips/cavium-octeon/smp.c b/arch/mips/cavium-octeon/smp.c
> index 89954f5f87fb..4212584e6efa 100644
> --- a/arch/mips/cavium-octeon/smp.c
> +++ b/arch/mips/cavium-octeon/smp.c
> @@ -20,6 +20,7 @@
>   #include <asm/mmu_context.h>
>   #include <asm/time.h>
>   #include <asm/setup.h>
> +#include <asm/smp.h>
>   
>   #include <asm/octeon/octeon.h>
>   
> diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
> index bcd6a944b839..6d69a9ba8167 100644
> --- a/arch/mips/kernel/smp-cps.c
> +++ b/arch/mips/kernel/smp-cps.c
> @@ -20,6 +20,7 @@
>   #include <asm/mipsregs.h>
>   #include <asm/pm-cps.h>
>   #include <asm/r4kcache.h>
> +#include <asm/smp.h>
>   #include <asm/smp-cps.h>
>   #include <asm/time.h>
>   #include <asm/uasm.h>
> diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
> index c81c2bd07c62..df8d789ede3c 100644
> --- a/arch/mips/loongson64/smp.c
> +++ b/arch/mips/loongson64/smp.c
> @@ -14,6 +14,7 @@
>   #include <linux/cpufreq.h>
>   #include <linux/kexec.h>
>   #include <asm/processor.h>
> +#include <asm/smp.h>
>   #include <asm/time.h>
>   #include <asm/tlbflush.h>
>   #include <asm/cacheflush.h>

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

Thanks.

[PATCH v2.1 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Josh Poimboeuf]

Include <asm/smp.h> to make sure play_dead() matches its prototype going
forward.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/mips/cavium-octeon/smp.c | 1 +
 arch/mips/kernel/smp-bmips.c  | 1 +
 arch/mips/kernel/smp-cps.c    | 1 +
 arch/mips/loongson64/smp.c    | 1 +
 4 files changed, 4 insertions(+)

diff --git a/arch/mips/cavium-octeon/smp.c b/arch/mips/cavium-octeon/smp.c
index 89954f5f87fb..4212584e6efa 100644
--- a/arch/mips/cavium-octeon/smp.c
+++ b/arch/mips/cavium-octeon/smp.c
@@ -20,6 +20,7 @@
 #include <asm/mmu_context.h>
 #include <asm/time.h>
 #include <asm/setup.h>
+#include <asm/smp.h>
 
 #include <asm/octeon/octeon.h>
 
diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
index f5d7bfa3472a..df9158e8329d 100644
--- a/arch/mips/kernel/smp-bmips.c
+++ b/arch/mips/kernel/smp-bmips.c
@@ -38,6 +38,7 @@
 #include <asm/traps.h>
 #include <asm/barrier.h>
 #include <asm/cpu-features.h>
+#include <asm/smp.h>
 
 static int __maybe_unused max_cpus = 1;
 
diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index bcd6a944b839..6d69a9ba8167 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -20,6 +20,7 @@
 #include <asm/mipsregs.h>
 #include <asm/pm-cps.h>
 #include <asm/r4kcache.h>
+#include <asm/smp.h>
 #include <asm/smp-cps.h>
 #include <asm/time.h>
 #include <asm/uasm.h>
diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
index 660e1de4412a..4e24b317e7cb 100644
--- a/arch/mips/loongson64/smp.c
+++ b/arch/mips/loongson64/smp.c
@@ -14,6 +14,7 @@
 #include <linux/cpufreq.h>
 #include <linux/kexec.h>
 #include <asm/processor.h>
+#include <asm/smp.h>
 #include <asm/time.h>
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>
-- 
2.39.1

Re: [PATCH v2.1 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Josh Poimboeuf]

On Thu, Feb 16, 2023 at 10:42:52AM -0800, Josh Poimboeuf wrote:
> Include <asm/smp.h> to make sure play_dead() matches its prototype going
> forward.
> 
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

The latest version of this patch triggered a new kbuild warning which is
fixed by the below patch.  If there are no objections I'll bundle it in
with the rest of the set for merging.

---8<---

Subject: [PATCH] mips/smp: Add CONFIG_SMP guard for raw_smp_processor_id()
Content-type: text/plain

Without CONFIG_SMP, raw_smp_processor_id() is not expected to be defined
by the arch.

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202302220755.HM8J8GOR-lkp@intel.com/
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/mips/include/asm/smp.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
index 4eee29b7845c..cf992b8b1e46 100644
--- a/arch/mips/include/asm/smp.h
+++ b/arch/mips/include/asm/smp.h
@@ -25,6 +25,7 @@ extern cpumask_t cpu_sibling_map[];
 extern cpumask_t cpu_core_map[];
 extern cpumask_t cpu_foreign_map[];
 
+#ifdef CONFIG_SMP
 static inline int raw_smp_processor_id(void)
 {
 #if defined(__VDSO__)
@@ -36,6 +37,7 @@ static inline int raw_smp_processor_id(void)
 #endif
 }
 #define raw_smp_processor_id raw_smp_processor_id
+#endif
 
 /* Map from cpu id to sequential logical cpu number.  This will only
    not be idempotent when cpus failed to come on-line.	*/
-- 
2.39.1

Re: [PATCH v2.1 09/24] mips/cpu: Expose play_dead()'s prototype definition

[Philippe Mathieu-Daudé]

On 1/3/23 19:16, Josh Poimboeuf wrote:

> The latest version of this patch triggered a new kbuild warning which is
> fixed by the below patch.  If there are no objections I'll bundle it in
> with the rest of the set for merging.
> 
> ---8<---
> 
> Subject: [PATCH] mips/smp: Add CONFIG_SMP guard for raw_smp_processor_id()
> Content-type: text/plain
> 
> Without CONFIG_SMP, raw_smp_processor_id() is not expected to be defined
> by the arch.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/oe-kbuild-all/202302220755.HM8J8GOR-lkp@intel.com/
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>   arch/mips/include/asm/smp.h | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
> index 4eee29b7845c..cf992b8b1e46 100644
> --- a/arch/mips/include/asm/smp.h
> +++ b/arch/mips/include/asm/smp.h
> @@ -25,6 +25,7 @@ extern cpumask_t cpu_sibling_map[];
>   extern cpumask_t cpu_core_map[];
>   extern cpumask_t cpu_foreign_map[];
>   
> +#ifdef CONFIG_SMP
>   static inline int raw_smp_processor_id(void)
>   {
>   #if defined(__VDSO__)
> @@ -36,6 +37,7 @@ static inline int raw_smp_processor_id(void)
>   #endif
>   }
>   #define raw_smp_processor_id raw_smp_processor_id
> +#endif
>   
>   /* Map from cpu id to sequential logical cpu number.  This will only
>      not be idempotent when cpus failed to come on-line.	*/

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

[PATCH v2 10/24] mips/cpu: Make sure play_dead() doesn't return

[Josh Poimboeuf]

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.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/mips/kernel/smp-bmips.c | 2 ++
 arch/mips/loongson64/smp.c   | 1 +
 2 files changed, 3 insertions(+)

diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
index df9158e8329d..be85fa075830 100644
--- a/arch/mips/kernel/smp-bmips.c
+++ b/arch/mips/kernel/smp-bmips.c
@@ -414,6 +414,8 @@ void __ref play_dead(void)
 	"	wait\n"
 	"	j	bmips_secondary_reentry\n"
 	: : : "memory");
+
+	BUG();
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */
diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
index 660e1de4412a..c81c2bd07c62 100644
--- a/arch/mips/loongson64/smp.c
+++ b/arch/mips/loongson64/smp.c
@@ -822,6 +822,7 @@ void play_dead(void)
 	state_addr = &per_cpu(cpu_state, cpu);
 	mb();
 	play_dead_at_ckseg1(state_addr);
+	BUG();
 }
 
 static int loongson3_disable_clock(unsigned int cpu)
-- 
2.39.1

Re: [PATCH v2 10/24] mips/cpu: Make sure play_dead() doesn't return

[Philippe Mathieu-Daudé]

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.
> 
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>   arch/mips/kernel/smp-bmips.c | 2 ++
>   arch/mips/loongson64/smp.c   | 1 +
>   2 files changed, 3 insertions(+)

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

[PATCH v2 11/24] mips/cpu: Mark play_dead() __noreturn

[Josh Poimboeuf]

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

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/mips/include/asm/smp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
index 5d9ff61004ca..4eee29b7845c 100644
--- a/arch/mips/include/asm/smp.h
+++ b/arch/mips/include/asm/smp.h
@@ -88,7 +88,7 @@ static inline void __cpu_die(unsigned int cpu)
 	mp_ops->cpu_die(cpu);
 }
 
-extern void play_dead(void);
+extern void __noreturn play_dead(void);
 #endif
 
 #ifdef CONFIG_KEXEC
-- 
2.39.1

Re: [PATCH v2 11/24] mips/cpu: Mark play_dead() __noreturn

[Philippe Mathieu-Daudé]

On 14/2/23 08:05, Josh Poimboeuf wrote:
> play_dead() doesn't return.  Annotate it as such.  By extension this
> also makes arch_cpu_idle_dead() noreturn.
> 
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>   arch/mips/include/asm/smp.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

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

[PATCH v2 12/24] powerpc/cpu: Mark start_secondary_resume() __noreturn

[Josh Poimboeuf]

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

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/powerpc/include/asm/smp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index f63505d74932..cfd42ca8765c 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -66,7 +66,7 @@ void start_secondary(void *unused);
 extern int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us);
 extern int smp_send_safe_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us);
 extern void smp_send_debugger_break(void);
-extern void start_secondary_resume(void);
+extern void __noreturn start_secondary_resume(void);
 extern void smp_generic_give_timebase(void);
 extern void smp_generic_take_timebase(void);
 
-- 
2.39.1

Re: [PATCH v2 12/24] powerpc/cpu: Mark start_secondary_resume() __noreturn

[Christophe Leroy]

Le 14/02/2023 à 08:05, Josh Poimboeuf a écrit :
> start_secondary_resume() doesn't return.  Annotate it as such.  By
> extension this also makes arch_cpu_idle_dead() noreturn.
> 
> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
>   arch/powerpc/include/asm/smp.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> index f63505d74932..cfd42ca8765c 100644
> --- a/arch/powerpc/include/asm/smp.h
> +++ b/arch/powerpc/include/asm/smp.h
> @@ -66,7 +66,7 @@ void start_secondary(void *unused);
>   extern int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us);
>   extern int smp_send_safe_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us);
>   extern void smp_send_debugger_break(void);
> -extern void start_secondary_resume(void);
> +extern void __noreturn start_secondary_resume(void);

Would have been a good opportunity to drop the pointless 'extern' keyword.

Checkpatch reports:

CHECK: extern prototypes should be avoided in .h files
#19: FILE: arch/powerpc/include/asm/smp.h:69:
+extern void __noreturn start_secondary_resume(void);


>   extern void smp_generic_give_timebase(void);
>   extern void smp_generic_take_timebase(void);
>   

[PATCH v2 13/24] sh/cpu: Make sure play_dead() doesn't return

[Josh Poimboeuf]

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@kernel.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();
 }
 
 extern void register_smp_ops(struct plat_smp_ops *ops);
-- 
2.39.1

Re: [PATCH v2 13/24] sh/cpu: Make sure play_dead() doesn't return

[Philippe Mathieu-Daudé]

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@kernel.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?

Re: [PATCH v2 13/24] sh/cpu: Make sure play_dead() doesn't return

[Josh Poimboeuf]

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@kernel.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

[PATCH v2 14/24] sh/cpu: Mark play_dead() __noreturn

[Josh Poimboeuf]

play_dead() 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/sh/include/asm/smp-ops.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/sh/include/asm/smp-ops.h b/arch/sh/include/asm/smp-ops.h
index 63866b1595a0..97331fcb7b85 100644
--- a/arch/sh/include/asm/smp-ops.h
+++ b/arch/sh/include/asm/smp-ops.h
@@ -24,7 +24,7 @@ static inline void plat_smp_setup(void)
 	mp_ops->smp_setup();
 }
 
-static inline void play_dead(void)
+static inline void __noreturn play_dead(void)
 {
 	mp_ops->play_dead();
 	BUG();
@@ -43,7 +43,7 @@ static inline void register_smp_ops(struct plat_smp_ops *ops)
 {
 }
 
-static inline void play_dead(void)
+static inline void __noreturn play_dead(void)
 {
 	BUG();
 }
-- 
2.39.1

[PATCH v2 15/24] sh/cpu: Expose arch_cpu_idle_dead()'s prototype definition

[Josh Poimboeuf]

Include <linux/cpu.h> to make sure arch_cpu_idle_dead() matches its
prototype going forward.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/sh/kernel/idle.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/sh/kernel/idle.c b/arch/sh/kernel/idle.c
index 3418c40f0099..114f0c4abeac 100644
--- a/arch/sh/kernel/idle.c
+++ b/arch/sh/kernel/idle.c
@@ -4,6 +4,7 @@
  *
  *  Copyright (C) 2002 - 2009  Paul Mundt
  */
+#include <linux/cpu.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/mm.h>
-- 
2.39.1

[PATCH v2 16/24] sparc/cpu: Mark cpu_play_dead() __noreturn

[Josh Poimboeuf]

cpu_play_dead() 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/sparc/include/asm/smp_64.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/sparc/include/asm/smp_64.h b/arch/sparc/include/asm/smp_64.h
index e75783b6abc4..505b6700805d 100644
--- a/arch/sparc/include/asm/smp_64.h
+++ b/arch/sparc/include/asm/smp_64.h
@@ -49,7 +49,7 @@ int hard_smp_processor_id(void);
 
 void smp_fill_in_cpu_possible_map(void);
 void smp_fill_in_sib_core_maps(void);
-void cpu_play_dead(void);
+void __noreturn cpu_play_dead(void);
 
 void smp_fetch_global_regs(void);
 void smp_fetch_global_pmu(void);
-- 
2.39.1

Re: [PATCH v2 16/24] sparc/cpu: Mark cpu_play_dead() __noreturn

[Philippe Mathieu-Daudé]

On 14/2/23 08:05, Josh Poimboeuf wrote:
> cpu_play_dead() 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/sparc/include/asm/smp_64.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

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

[PATCH v2 17/24] x86/cpu: Make sure play_dead() doesn't return

[Josh Poimboeuf]

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@kernel.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();
 }
 
 static inline void smp_send_reschedule(int cpu)
-- 
2.39.1

Re: [PATCH v2 17/24] x86/cpu: Make sure play_dead() doesn't return

[Philippe Mathieu-Daudé]

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@kernel.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.

[PATCH v2 18/24] x86/cpu: Mark play_dead() __noreturn

[Josh Poimboeuf]

play_dead() 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/x86/include/asm/smp.h | 2 +-
 arch/x86/kernel/process.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 8f628e08b25a..e6d1d2810e38 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -93,7 +93,7 @@ static inline void __cpu_die(unsigned int cpu)
 	smp_ops.cpu_die(cpu);
 }
 
-static inline void play_dead(void)
+static inline void __noreturn play_dead(void)
 {
 	smp_ops.play_dead();
 	BUG();
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index e57cd31bfec4..4433d13edd44 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -715,7 +715,7 @@ static bool x86_idle_set(void)
 }
 
 #ifndef CONFIG_SMP
-static inline void play_dead(void)
+static inline void __noreturn play_dead(void)
 {
 	BUG();
 }
-- 
2.39.1

[PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Josh Poimboeuf]

cpu_die() 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@kernel.org>
---
 arch/xtensa/kernel/smp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
index 4dc109dd6214..7bad78495536 100644
--- a/arch/xtensa/kernel/smp.c
+++ b/arch/xtensa/kernel/smp.c
@@ -341,6 +341,8 @@ void __ref cpu_die(void)
 	__asm__ __volatile__(
 			"	movi	a2, cpu_restart\n"
 			"	jx	a2\n");
+
+	BUG();
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */
-- 
2.39.1

Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Philippe Mathieu-Daudé]

Hi Josh,

On 14/2/23 08:05, Josh Poimboeuf wrote:
> cpu_die() 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@kernel.org>
> ---
>   arch/xtensa/kernel/smp.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
> index 4dc109dd6214..7bad78495536 100644
> --- a/arch/xtensa/kernel/smp.c
> +++ b/arch/xtensa/kernel/smp.c

Can you update the documentation along? Currently we have:

   /*
    * Called from the idle thread for the CPU which has been shutdown.
    *
    * Note that we disable IRQs here, but do not re-enable them
    * before returning to the caller. This is also the behaviour
    * of the other hotplug-cpu capable cores, so presumably coming
    * out of idle fixes this.
    */

> @@ -341,6 +341,8 @@ void __ref cpu_die(void)
>   	__asm__ __volatile__(
>   			"	movi	a2, cpu_restart\n"
>   			"	jx	a2\n");
> +
> +	BUG();
>   }
>   
>   #endif /* CONFIG_HOTPLUG_CPU */

Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Josh Poimboeuf]

On Tue, Feb 14, 2023 at 08:55:32AM +0100, Philippe Mathieu-Daudé wrote:
> Hi Josh,
> 
> On 14/2/23 08:05, Josh Poimboeuf wrote:
> > cpu_die() 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@kernel.org>
> > ---
> >   arch/xtensa/kernel/smp.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
> > index 4dc109dd6214..7bad78495536 100644
> > --- a/arch/xtensa/kernel/smp.c
> > +++ b/arch/xtensa/kernel/smp.c
> 
> Can you update the documentation along? Currently we have:
> 
>   /*
>    * Called from the idle thread for the CPU which has been shutdown.
>    *
>    * Note that we disable IRQs here, but do not re-enable them
>    * before returning to the caller. This is also the behaviour
>    * of the other hotplug-cpu capable cores, so presumably coming
>    * out of idle fixes this.
>    */

void __ref cpu_die(void)
{
	idle_task_exit();
	local_irq_disable();
	__asm__ __volatile__(
			"	movi	a2, cpu_restart\n"
			"	jx	a2\n");

	BUG();
}

Hm, not only is the comment wrong, but it seems to be branching to
cpu_restart?  That doesn't seem right at all.

Max/Chris?

-- 
Josh

Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Steven Rostedt]

On Tue, 14 Feb 2023 10:23:22 -0800
Josh Poimboeuf <jpoimboe@kernel.org> wrote:


> void __ref cpu_die(void)
> {
> 	idle_task_exit();
> 	local_irq_disable();
> 	__asm__ __volatile__(
> 			"	movi	a2, cpu_restart\n"
> 			"	jx	a2\n");
> 
> 	BUG();
> }
> 
> Hm, not only is the comment wrong, but it seems to be branching to
> cpu_restart?  That doesn't seem right at all.

Agreed, that does not look right at all.

-- Steve

> 
> Max/Chris?
> 

Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Max Filippov]

On Tue, Feb 14, 2023 at 10:23 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> On Tue, Feb 14, 2023 at 08:55:32AM +0100, Philippe Mathieu-Daudé wrote:
> > Can you update the documentation along? Currently we have:
> >
> >   /*
> >    * Called from the idle thread for the CPU which has been shutdown.
> >    *
> >    * Note that we disable IRQs here, but do not re-enable them
> >    * before returning to the caller. This is also the behaviour
> >    * of the other hotplug-cpu capable cores, so presumably coming
> >    * out of idle fixes this.
> >    */
>
> void __ref cpu_die(void)
> {
>         idle_task_exit();
>         local_irq_disable();
>         __asm__ __volatile__(
>                         "       movi    a2, cpu_restart\n"
>                         "       jx      a2\n");
>
>         BUG();
> }
>
> Hm, not only is the comment wrong, but it seems to be branching to
> cpu_restart?  That doesn't seem right at all.

Perhaps the name is a bit misleading. The CPU that enters 'cpu_restart'
loops there until a call to 'boot_secondary' releases it, after which it goes
to '_startup'. So it is a restart, but not immediate.

-- 
Thanks.
-- Max

Re: [PATCH v2 19/24] xtensa/cpu: Make sure cpu_die() doesn't return

[Josh Poimboeuf]

On Tue, Feb 14, 2023 at 11:48:41AM -0800, Max Filippov wrote:
> On Tue, Feb 14, 2023 at 10:23 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> > On Tue, Feb 14, 2023 at 08:55:32AM +0100, Philippe Mathieu-Daudé wrote:
> > > Can you update the documentation along? Currently we have:
> > >
> > >   /*
> > >    * Called from the idle thread for the CPU which has been shutdown.
> > >    *
> > >    * Note that we disable IRQs here, but do not re-enable them
> > >    * before returning to the caller. This is also the behaviour
> > >    * of the other hotplug-cpu capable cores, so presumably coming
> > >    * out of idle fixes this.
> > >    */
> >
> > void __ref cpu_die(void)
> > {
> >         idle_task_exit();
> >         local_irq_disable();
> >         __asm__ __volatile__(
> >                         "       movi    a2, cpu_restart\n"
> >                         "       jx      a2\n");
> >
> >         BUG();
> > }
> >
> > Hm, not only is the comment wrong, but it seems to be branching to
> > cpu_restart?  That doesn't seem right at all.
> 
> Perhaps the name is a bit misleading. The CPU that enters 'cpu_restart'
> loops there until a call to 'boot_secondary' releases it, after which it goes
> to '_startup'. So it is a restart, but not immediate.

Ah, I see.  That sounds similar to what Xen does.

-- 
Josh

[PATCH v2 20/24] xtensa/cpu: Mark cpu_die() __noreturn

[Josh Poimboeuf]

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/xtensa/include/asm/smp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/xtensa/include/asm/smp.h b/arch/xtensa/include/asm/smp.h
index 4e43f5643891..5dc5bf8cdd77 100644
--- a/arch/xtensa/include/asm/smp.h
+++ b/arch/xtensa/include/asm/smp.h
@@ -33,7 +33,7 @@ void show_ipi_list(struct seq_file *p, int prec);
 
 void __cpu_die(unsigned int cpu);
 int __cpu_disable(void);
-void cpu_die(void);
+void __noreturn cpu_die(void);
 void cpu_restart(void);
 
 #endif /* CONFIG_HOTPLUG_CPU */
-- 
2.39.1

Re: [PATCH v2 20/24] xtensa/cpu: Mark cpu_die() __noreturn

[Max Filippov]

On Mon, Feb 13, 2023 at 11:07 PM Josh Poimboeuf <jpoimboe@kernel.org> 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/xtensa/include/asm/smp.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Max Filippov <jcmvbkbc@gmail.com>

-- 
Thanks.
-- Max

[PATCH v2 21/24] sched/idle: Make sure weak version of arch_cpu_idle_dead() doesn't return

[Josh Poimboeuf]

arch_cpu_idle_dead() should never return.  Make it so.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 kernel/sched/idle.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index e9ef66be2870..56e152f06d0f 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -75,7 +75,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
 void __weak arch_cpu_idle_prepare(void) { }
 void __weak arch_cpu_idle_enter(void) { }
 void __weak arch_cpu_idle_exit(void) { }
-void __weak arch_cpu_idle_dead(void) { }
+void __weak arch_cpu_idle_dead(void) { while (1); }
 void __weak arch_cpu_idle(void)
 {
 	cpu_idle_force_poll = 1;
-- 
2.39.1

[PATCH v2 22/24] objtool: Include weak functions in 'global_noreturns' check

[Josh Poimboeuf]

If a global __noreturn function prototype has a corresponding weak
function, it should also be __noreturn.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ba07a8ebaf73..0a1cf867d9b2 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -193,14 +193,14 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 	if (!func)
 		return false;
 
-	if (func->bind == STB_WEAK)
-		return false;
-
-	if (func->bind == STB_GLOBAL)
+	if (func->bind == STB_GLOBAL || func->bind == STB_WEAK)
 		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 			if (!strcmp(func->name, global_noreturns[i]))
 				return true;
 
+	if (func->bind == STB_WEAK)
+		return false;
+
 	if (!func->len)
 		return false;
 
-- 
2.39.1

[PATCH v2 23/24] init: Make arch_call_rest_init() and rest_init() __noreturn

[Josh Poimboeuf]

arch_call_rest_init() and rest_init() don't return.  Annotate them as
such.

Fixes the following warning:

  init/main.o: warning: objtool: start_kernel+0x4ad: unreachable instruction

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/s390/kernel/setup.c     | 2 +-
 include/linux/start_kernel.h | 4 ++--
 init/main.c                  | 4 ++--
 tools/objtool/check.c        | 2 ++
 4 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 696c9e007a36..85abff362f29 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -393,7 +393,7 @@ int __init arch_early_irq_init(void)
 	return 0;
 }
 
-void __init arch_call_rest_init(void)
+void __init __noreturn arch_call_rest_init(void)
 {
 	unsigned long stack;
 
diff --git a/include/linux/start_kernel.h b/include/linux/start_kernel.h
index 8b369a41c03c..864921e54c92 100644
--- a/include/linux/start_kernel.h
+++ b/include/linux/start_kernel.h
@@ -9,7 +9,7 @@
    up something else. */
 
 extern asmlinkage void __init start_kernel(void);
-extern void __init arch_call_rest_init(void);
-extern void __ref rest_init(void);
+extern void __init __noreturn arch_call_rest_init(void);
+extern void __ref __noreturn rest_init(void);
 
 #endif /* _LINUX_START_KERNEL_H */
diff --git a/init/main.c b/init/main.c
index e1c3911d7c70..ef71a9902e47 100644
--- a/init/main.c
+++ b/init/main.c
@@ -683,7 +683,7 @@ static void __init setup_command_line(char *command_line)
 
 static __initdata DECLARE_COMPLETION(kthreadd_done);
 
-noinline void __ref rest_init(void)
+noinline void __ref __noreturn rest_init(void)
 {
 	struct task_struct *tsk;
 	int pid;
@@ -889,7 +889,7 @@ static int __init early_randomize_kstack_offset(char *buf)
 early_param("randomize_kstack_offset", early_randomize_kstack_offset);
 #endif
 
-void __init __weak arch_call_rest_init(void)
+void __init __weak __noreturn arch_call_rest_init(void)
 {
 	rest_init();
 }
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 0a1cf867d9b2..f79baae3e338 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -167,6 +167,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"__reiserfs_panic",
 		"__stack_chk_fail",
 		"__ubsan_handle_builtin_unreachable",
+		"arch_call_rest_init",
 		"cpu_bringup_and_idle",
 		"cpu_startup_entry",
 		"do_exit",
@@ -181,6 +182,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"machine_real_restart",
 		"make_task_dead",
 		"panic",
+		"rest_init",
 		"rewind_stack_and_make_dead",
 		"sev_es_terminate",
 		"snp_abort",
-- 
2.39.1

[PATCH v2 24/24] sched/idle: Mark arch_cpu_idle_dead() __noreturn

[Josh Poimboeuf]

Before commit 076cbf5d2163 ("x86/xen: don't let xen_pv_play_dead()
return"), in Xen, when a previously offlined CPU was brought back
online, it unexpectedly resumed execution where it left off in the
middle of the idle loop.

There were some hacks to make that work, but the behavior was surprising
as do_idle() doesn't expect an offlined CPU to return from the dead (in
arch_cpu_idle_dead()).

Now that Xen has been fixed, and the arch-specific implementations of
arch_cpu_idle_dead() also don't return, give it a __noreturn attribute.

This will cause the compiler to complain if an arch-specific
implementation might return.  It also improves code generation for both
caller and callee.

Also fixes the following warning:

  vmlinux.o: warning: objtool: do_idle+0x25f: unreachable instruction

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/alpha/kernel/process.c     | 2 +-
 arch/arm/kernel/smp.c           | 2 +-
 arch/arm64/kernel/process.c     | 2 +-
 arch/csky/kernel/smp.c          | 2 +-
 arch/ia64/kernel/process.c      | 2 +-
 arch/loongarch/kernel/process.c | 2 +-
 arch/mips/kernel/process.c      | 2 +-
 arch/parisc/kernel/process.c    | 2 +-
 arch/powerpc/kernel/smp.c       | 2 +-
 arch/riscv/kernel/cpu-hotplug.c | 2 +-
 arch/s390/kernel/idle.c         | 2 +-
 arch/sh/kernel/idle.c           | 2 +-
 arch/sparc/kernel/process_64.c  | 2 +-
 arch/x86/kernel/process.c       | 2 +-
 arch/xtensa/kernel/smp.c        | 2 +-
 include/linux/cpu.h             | 2 +-
 kernel/sched/idle.c             | 2 +-
 tools/objtool/check.c           | 1 +
 18 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index d0ff06eda8fa..9bae2fc4910f 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -60,7 +60,7 @@ void arch_cpu_idle(void)
 	wtint(0);
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	wtint(INT_MAX);
 	BUG();
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index adcd417c526b..c2daa0f2f784 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -320,7 +320,7 @@ void __cpu_die(unsigned int cpu)
  * of the other hotplug-cpu capable cores, so presumably coming
  * out of idle fixes this.
  */
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	unsigned int cpu = smp_processor_id();
 
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 269ac1c25ae2..8d606bbb4a9a 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -69,7 +69,7 @@ void (*pm_power_off)(void);
 EXPORT_SYMBOL_GPL(pm_power_off);
 
 #ifdef CONFIG_HOTPLUG_CPU
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
        cpu_die();
 }
diff --git a/arch/csky/kernel/smp.c b/arch/csky/kernel/smp.c
index 0ec20efaf5fd..9c7a20b73ac6 100644
--- a/arch/csky/kernel/smp.c
+++ b/arch/csky/kernel/smp.c
@@ -300,7 +300,7 @@ void __cpu_die(unsigned int cpu)
 	pr_notice("CPU%u: shutdown\n", cpu);
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	idle_task_exit();
 
diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index 78f5794b2dde..9a5cd9fad3a9 100644
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -225,7 +225,7 @@ static inline void __noreturn play_dead(void)
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	play_dead();
 }
diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
index edfd220a3737..ba70e94eb996 100644
--- a/arch/loongarch/kernel/process.c
+++ b/arch/loongarch/kernel/process.c
@@ -61,7 +61,7 @@ unsigned long boot_option_idle_override = IDLE_NO_OVERRIDE;
 EXPORT_SYMBOL(boot_option_idle_override);
 
 #ifdef CONFIG_HOTPLUG_CPU
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	play_dead();
 }
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 093dbbd6b843..a3225912c862 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -40,7 +40,7 @@
 #include <asm/stacktrace.h>
 
 #ifdef CONFIG_HOTPLUG_CPU
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	play_dead();
 }
diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index c064719b49b0..97c6f875bd0e 100644
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -159,7 +159,7 @@ EXPORT_SYMBOL(running_on_qemu);
 /*
  * Called from the idle thread for the CPU which has been shutdown.
  */
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	idle_task_exit();
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 6b90f10a6c81..f62e5e651bcd 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1752,7 +1752,7 @@ void __cpu_die(unsigned int cpu)
 		smp_ops->cpu_die(cpu);
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	/*
 	 * Disable on the down path. This will be re-enabled by
diff --git a/arch/riscv/kernel/cpu-hotplug.c b/arch/riscv/kernel/cpu-hotplug.c
index f7a832e3a1d1..59b80211c25f 100644
--- a/arch/riscv/kernel/cpu-hotplug.c
+++ b/arch/riscv/kernel/cpu-hotplug.c
@@ -71,7 +71,7 @@ void __cpu_die(unsigned int cpu)
 /*
  * Called from the idle thread for the CPU which has been shutdown.
  */
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	idle_task_exit();
 
diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index b04fb418307c..45b5ee28dbe3 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -143,7 +143,7 @@ void arch_cpu_idle_exit(void)
 {
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	cpu_die();
 }
diff --git a/arch/sh/kernel/idle.c b/arch/sh/kernel/idle.c
index 114f0c4abeac..d662503b0665 100644
--- a/arch/sh/kernel/idle.c
+++ b/arch/sh/kernel/idle.c
@@ -30,7 +30,7 @@ void default_idle(void)
 	clear_bl_bit();
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	play_dead();
 }
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index 91c2b8124527..b51d8fb0ecdc 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -95,7 +95,7 @@ void arch_cpu_idle(void)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	sched_preempt_enable_no_resched();
 	cpu_play_dead();
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 4433d13edd44..e52158263d30 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -727,7 +727,7 @@ void arch_cpu_idle_enter(void)
 	local_touch_nmi();
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	play_dead();
 }
diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
index 7bad78495536..054bd64eab19 100644
--- a/arch/xtensa/kernel/smp.c
+++ b/arch/xtensa/kernel/smp.c
@@ -322,7 +322,7 @@ void __cpu_die(unsigned int cpu)
 	pr_err("CPU%u: unable to kill\n", cpu);
 }
 
-void arch_cpu_idle_dead(void)
+void __noreturn arch_cpu_idle_dead(void)
 {
 	cpu_die();
 }
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index f83e4519c5f0..8582a7142623 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -182,7 +182,7 @@ void arch_cpu_idle(void);
 void arch_cpu_idle_prepare(void);
 void arch_cpu_idle_enter(void);
 void arch_cpu_idle_exit(void);
-void arch_cpu_idle_dead(void);
+void __noreturn arch_cpu_idle_dead(void);
 
 int cpu_report_state(int cpu);
 int cpu_check_up_prepare(int cpu);
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 56e152f06d0f..342f58a329f5 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -75,7 +75,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
 void __weak arch_cpu_idle_prepare(void) { }
 void __weak arch_cpu_idle_enter(void) { }
 void __weak arch_cpu_idle_exit(void) { }
-void __weak arch_cpu_idle_dead(void) { while (1); }
+void __weak __noreturn arch_cpu_idle_dead(void) { while (1); }
 void __weak arch_cpu_idle(void)
 {
 	cpu_idle_force_poll = 1;
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f79baae3e338..4be38a40aaca 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -168,6 +168,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"__stack_chk_fail",
 		"__ubsan_handle_builtin_unreachable",
 		"arch_call_rest_init",
+		"arch_cpu_idle_dead",
 		"cpu_bringup_and_idle",
 		"cpu_startup_entry",
 		"do_exit",
-- 
2.39.1

Re: [PATCH v2 00/24] cpu,sched: Mark arch_cpu_idle_dead() __noreturn

[Philippe Mathieu-Daudé]

On 14/2/23 08:05, Josh Poimboeuf wrote:
> v2:
> - make arch_call_rest_init() and rest_init() __noreturn
> - make objtool 'global_returns' work for weak functions
> - rebase on tip/objtool/core with dependencies merged in (mingo)
> - add acks
> 
> v1.1:
> - add __noreturn to all arch_cpu_idle_dead() implementations (mpe)

Possible similar candidates: panic_smp_self_stop, nmi_panic_self_stop
and kexec.

Re: [PATCH v2 00/24] cpu,sched: Mark arch_cpu_idle_dead() __noreturn

[Josh Poimboeuf]

On Tue, Feb 14, 2023 at 10:25:50AM +0100, Philippe Mathieu-Daudé wrote:
> On 14/2/23 08:05, Josh Poimboeuf wrote:
> > v2:
> > - make arch_call_rest_init() and rest_init() __noreturn
> > - make objtool 'global_returns' work for weak functions
> > - rebase on tip/objtool/core with dependencies merged in (mingo)
> > - add acks
> > 
> > v1.1:
> > - add __noreturn to all arch_cpu_idle_dead() implementations (mpe)
> 
> Possible similar candidates: panic_smp_self_stop, nmi_panic_self_stop
> and kexec.

Agreed.  Any volunteers?

-- 
Josh

Re: [PATCH v2 00/24] cpu,sched: Mark arch_cpu_idle_dead() __noreturn

[Paul E. McKenney]

On Mon, Feb 13, 2023 at 11:05:34PM -0800, Josh Poimboeuf wrote:
> v2:
> - make arch_call_rest_init() and rest_init() __noreturn
> - make objtool 'global_returns' work for weak functions
> - rebase on tip/objtool/core with dependencies merged in (mingo)
> - add acks
> 
> v1.1:
> - add __noreturn to all arch_cpu_idle_dead() implementations (mpe)

With this, rcutorture no longer gets objtool complaints on x86, thank you!

Tested-by: Paul E. McKenney <paulmck@kernel.org>

> Josh Poimboeuf (24):
>   alpha/cpu: Expose arch_cpu_idle_dead()'s prototype declaration
>   alpha/cpu: Make sure arch_cpu_idle_dead() doesn't return
>   arm/cpu: Make sure arch_cpu_idle_dead() doesn't return
>   arm64/cpu: Mark cpu_die() __noreturn
>   csky/cpu: Make sure arch_cpu_idle_dead() doesn't return
>   ia64/cpu: Mark play_dead() __noreturn
>   loongarch/cpu: Make sure play_dead() doesn't return
>   loongarch/cpu: Mark play_dead() __noreturn
>   mips/cpu: Expose play_dead()'s prototype definition
>   mips/cpu: Make sure play_dead() doesn't return
>   mips/cpu: Mark play_dead() __noreturn
>   powerpc/cpu: Mark start_secondary_resume() __noreturn
>   sh/cpu: Make sure play_dead() doesn't return
>   sh/cpu: Mark play_dead() __noreturn
>   sh/cpu: Expose arch_cpu_idle_dead()'s prototype definition
>   sparc/cpu: Mark cpu_play_dead() __noreturn
>   x86/cpu: Make sure play_dead() doesn't return
>   x86/cpu: Mark play_dead() __noreturn
>   xtensa/cpu: Make sure cpu_die() doesn't return
>   xtensa/cpu: Mark cpu_die() __noreturn
>   sched/idle: Make sure weak version of arch_cpu_idle_dead() doesn't
>     return
>   objtool: Include weak functions in 'global_noreturns' check
>   init: Make arch_call_rest_init() and rest_init() __noreturn
>   sched/idle: Mark arch_cpu_idle_dead() __noreturn
> 
>  arch/alpha/kernel/process.c      |  4 +++-
>  arch/arm/kernel/smp.c            |  4 +++-
>  arch/arm64/include/asm/smp.h     |  2 +-
>  arch/arm64/kernel/process.c      |  2 +-
>  arch/csky/kernel/smp.c           |  4 +++-
>  arch/ia64/kernel/process.c       |  6 +++---
>  arch/loongarch/include/asm/smp.h |  2 +-
>  arch/loongarch/kernel/process.c  |  2 +-
>  arch/loongarch/kernel/smp.c      |  2 +-
>  arch/mips/include/asm/smp.h      |  2 +-
>  arch/mips/kernel/process.c       |  2 +-
>  arch/mips/kernel/smp-bmips.c     |  3 +++
>  arch/mips/loongson64/smp.c       |  1 +
>  arch/parisc/kernel/process.c     |  2 +-
>  arch/powerpc/include/asm/smp.h   |  2 +-
>  arch/powerpc/kernel/smp.c        |  2 +-
>  arch/riscv/kernel/cpu-hotplug.c  |  2 +-
>  arch/s390/kernel/idle.c          |  2 +-
>  arch/s390/kernel/setup.c         |  2 +-
>  arch/sh/include/asm/smp-ops.h    |  5 +++--
>  arch/sh/kernel/idle.c            |  3 ++-
>  arch/sparc/include/asm/smp_64.h  |  2 +-
>  arch/sparc/kernel/process_64.c   |  2 +-
>  arch/x86/include/asm/smp.h       |  3 ++-
>  arch/x86/kernel/process.c        |  4 ++--
>  arch/xtensa/include/asm/smp.h    |  2 +-
>  arch/xtensa/kernel/smp.c         |  4 +++-
>  include/linux/cpu.h              |  2 +-
>  include/linux/start_kernel.h     |  4 ++--
>  init/main.c                      |  4 ++--
>  kernel/sched/idle.c              |  2 +-
>  tools/objtool/check.c            | 11 +++++++----
>  32 files changed, 57 insertions(+), 39 deletions(-)
> 
> -- 
> 2.39.1
>