linux-kernel - Re: objtool warning for next-20221118

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Date:   Tue, 31 Jan 2023 16:33:11 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, sfr@...b.auug.org.au,
        linux-kernel@...r.kernel.org
Subject: Re: objtool warning for next-20221118

On Tue, Jan 31, 2023 at 04:02:47PM -0800, Josh Poimboeuf wrote:
> On Sat, Jan 28, 2023 at 11:06:34AM -0800, Paul E. McKenney wrote:
> > Sorry to be a nag, but I am still seeing this.  Not a huge problem because
> > I now filter it out so that it does not get in the way of other bugs,
> > but I figured that I should follow up.
> 
> Does this fix it? (works for me)

A quick touch test indicates that it does indeed fix it, thank you!

I am also rerunning the exact test setup that generated the original
warning, but I don't expect any nasty surprises.

							Thanx, Paul

> If so, I'll need to extend it for all arches.
> 
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 40d156a31676..5db0daba750f 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -712,6 +712,7 @@ void arch_cpu_idle_enter(void)
>  void arch_cpu_idle_dead(void)
>  {
>  	play_dead();
> +	BUG();
>  }
>  
>  /*
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 314802f98b9d..7fbbd1572288 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -185,7 +185,7 @@ 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 f26ab2675f7d..921b8b3e3d0c 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -71,7 +71,7 @@ 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;
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 4b7c8b33069e..a9cb925bf095 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_cpu_idle_dead",
>  		"cpu_bringup_and_idle",
>  		"cpu_startup_entry",
>  		"do_exit",