Date:   Tue, 31 Jan 2023 20:21:13 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Josh Poimboeuf <jpoimboe@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>, sfr@canb.auug.org.au,
        linux-kernel@vger.kernel.org
Subject: Re: objtool warning for next-20221118
Message-ID: <20230201042113.GA3871307@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
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On Tue, Jan 31, 2023 at 04:33:11PM -0800, Paul E. McKenney wrote:
> 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.

And no nasty surprises, again, thank you!

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

							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",