linux-kernel - Re: [BUG objtool,x86] Missing __noreturn annotation in acpi_processor_ffh_play

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Message-ID: <20250228220039.tjimagjqkswzooi4@jpoimboe>
Date: Fri, 28 Feb 2025 14:00:39 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: patryk.wlazlyn@...ux.intel.com, artem.bityutskiy@...ux.intel.com,
	dave.hansen@...ux.intel.com, gautham.shenoy@....com,
	rafael.j.wysocki@...el.com, linux-kernel@...r.kernel.org,
	sfr@...b.auug.org.au, peterz@...radead.org
Subject: Re: [BUG objtool,x86] Missing __noreturn annotation in
 acpi_processor_ffh_play_dead()

On Fri, Feb 28, 2025 at 11:51:26AM -0800, Paul E. McKenney wrote:
> On Fri, Feb 28, 2025 at 11:12:13AM -0800, Josh Poimboeuf wrote:
> > On Fri, Feb 28, 2025 at 11:00:07AM -0800, Paul E. McKenney wrote:
> > > Hello!
> > > 
> > > My recent -next testing hits this objtool complaint:
> > > 
> > > vmlinux.o: warning: objtool: acpi_idle_play_dead+0x3c: acpi_processor_ffh_play_dead() is missing a __noreturn annotation
> > > 
> > > My attempts to silence this by adding the suggested __noreturn annotations
> > > didn't help, and often got me compiler warnings about __noreturn functions
> > > actually returning.  So I bisected, which converges on this innocent-looking
> > > commit:
> > > 
> > > a7dd183f0b38 ("x86/smp: Allow calling mwait_play_dead with an arbitrary hint")
> > > 
> > > Several runs verified that this really is the commit that objtool is
> > > complaining about.  Unfortunately, this commit does not revert cleanly.
> > > 
> > > This is from builds using clang version 19.1.5 (CentOS 19.1.5-2.el9).
> > > 
> > > Help?
> > 
> > I can take a look.  Is it LLVM defconfig?  Otherwise can you send the
> > .config?
> 
> Thank you!  And rcutorture modifies whatever defconfig it gets. so please
> see below for the full .config.

With your config I actually get a different warning:

        vmlinux.o: warning: objtool: acpi_processor_ffh_play_dead+0x67: mwait_play_dead() is missing a __noreturn annotation

The below patch should fix both, can you confirm it fixes yours?

From: Josh Poimboeuf <jpoimboe@...nel.org>
Subject: [PATCH] x86/smp: Fix __noreturn annotations for mwait_play_dead() and
 acpi_processor_ffh_play_dead()

mwait_play_dead() doesn't return, but only has a partial __noreturn
annotation.

acpi_processor_ffh_play_dead() also doesn't return due to its
unconditional calling of mwait_play_dead().

Fix the annotations for both functions.

This fixes the following warnings:

  vmlinux.o: warning: objtool: acpi_processor_ffh_play_dead+0x67: mwait_play_dead() is missing a __noreturn annotation
  vmlinux.o: warning: objtool: acpi_idle_play_dead+0x3c: acpi_processor_ffh_play_dead() is missing a __noreturn annotation

Reported-by: "Paul E. McKenney" <paulmck@...nel.org>
Fixes: a7dd183f0b38 ("x86/smp: Allow calling mwait_play_dead with an arbitrary hint")
Fixes: 541ddf31e300 ("ACPI/processor_idle: Add FFH state handling")
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/include/asm/smp.h    | 2 +-
 arch/x86/kernel/acpi/cstate.c | 2 +-
 include/acpi/processor.h      | 2 +-
 tools/objtool/noreturns.h     | 2 ++
 4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 80f8bfd83fc7..9c7ae0a214dc 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -114,7 +114,7 @@ void wbinvd_on_cpu(int cpu);
 int wbinvd_on_all_cpus(void);
 
 void smp_kick_mwait_play_dead(void);
-void mwait_play_dead(unsigned int eax_hint);
+void __noreturn mwait_play_dead(unsigned int eax_hint);
 
 void native_smp_send_reschedule(int cpu);
 void native_send_call_func_ipi(const struct cpumask *mask);
diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index 86c87c01d23d..d25584255ab8 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -206,7 +206,7 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
 }
 EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
 
-void acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx)
+void __noreturn acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx)
 {
 	unsigned int cpu = smp_processor_id();
 	struct cstate_entry *percpu_entry;
diff --git a/include/acpi/processor.h b/include/acpi/processor.h
index 63a37e72b721..86b6b17b0f70 100644
--- a/include/acpi/processor.h
+++ b/include/acpi/processor.h
@@ -280,7 +280,7 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
 				    struct acpi_processor_cx *cx,
 				    struct acpi_power_register *reg);
 void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cstate);
-void acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx);
+void __noreturn acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx);
 #else
 static inline void acpi_processor_power_init_bm_check(struct
 						      acpi_processor_flags
diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
index b2174894f9f7..5a4aec4c4639 100644
--- a/tools/objtool/noreturns.h
+++ b/tools/objtool/noreturns.h
@@ -16,6 +16,7 @@ NORETURN(__tdx_hypercall_failed)
 NORETURN(__ubsan_handle_builtin_unreachable)
 NORETURN(__x64_sys_exit)
 NORETURN(__x64_sys_exit_group)
+NORETURN(acpi_processor_ffh_play_dead)
 NORETURN(arch_cpu_idle_dead)
 NORETURN(bch2_trans_in_restart_error)
 NORETURN(bch2_trans_restart_error)
@@ -34,6 +35,7 @@ NORETURN(kunit_try_catch_throw)
 NORETURN(machine_real_restart)
 NORETURN(make_task_dead)
 NORETURN(mpt_halt_firmware)
+NORETURN(mwait_play_dead)
 NORETURN(nmi_panic_self_stop)
 NORETURN(panic)
 NORETURN(panic_smp_self_stop)
-- 
2.48.1