x86/smp: Fix mwait_play_dead() and acpi_processor_ffh_play_dead() noreturn behavior [partial]

JIRA: https://issues.redhat.com/browse/RHEL-85522
Conflicts: RHEL doesn't have noreturns.h, so update global_no_returns[]
	   in tools/objtool/check.c

commit 4e32645
Author: Josh Poimboeuf <jpoimboe@kernel.org>
Date:   Sun Mar 2 16:48:51 2025 -0800

    x86/smp: Fix mwait_play_dead() and acpi_processor_ffh_play_dead() noreturn behavior

    Fix some related issues (done in a single patch to avoid introducing
    intermediate bisect warnings):

      1) The SMP version of mwait_play_dead() doesn't return, but its
         !SMP counterpart does.  Make its calling behavior consistent by
         resolving the !SMP version to a BUG().  It should never be called
         anyway, this just enforces that at runtime and enables its callers
         to be marked as __noreturn.

      2) While the SMP definition of mwait_play_dead() is annotated as
         __noreturn, the declaration isn't.  Nor is it listed in
         tools/objtool/noreturns.h.  Fix that.

      3) Similar to #1, the SMP version of acpi_processor_ffh_play_dead()
         doesn't return but its !SMP counterpart does.  Make the !SMP
         version a BUG().  It should never be called.

      4) acpi_processor_ffh_play_dead() doesn't return, but is lacking any
         __noreturn annotations.  Fix that.

    This fixes the following objtool 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

    Fixes: a7dd183 ("x86/smp: Allow calling mwait_play_dead with an arbitrary hint")
    Fixes: 541ddf3 ("ACPI/processor_idle: Add FFH state handling")
    Reported-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Tested-by: Paul E. McKenney <paulmck@kernel.org>
    Link: https://lore.kernel.org/r/e885c6fa9e96a61471b33e48c2162d28b15b14c5.1740962711.git.jpoimboe@kernel.org

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

arch/x86/include/asm/smp.h

@@ -119,7 +119,7 @@ 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);
@@ -171,7 +171,7 @@ static inline struct cpumask *cpu_llc_shared_mask(int cpu)
 	return (struct cpumask *)cpumask_of(0);
 }
 
-static inline void mwait_play_dead(unsigned int eax_hint) { }
+static inline void __noreturn mwait_play_dead(unsigned int eax_hint) { BUG(); }
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_DEBUG_NMI_SELFTEST

arch/x86/kernel/acpi/cstate.c

@@ -205,7 +205,7 @@ 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;

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
@@ -301,9 +301,9 @@ static inline void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx
 {
 	return;
 }
-static inline void acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx)
+static inline void __noreturn acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx)
 {
-	return;
+	BUG();
 }
 #endif
 

tools/objtool/check.c

@@ -205,6 +205,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"machine_real_restart",
 		"make_task_dead",
 		"mpt_halt_firmware",
+		"mwait_play_dead",
 		"nmi_panic_self_stop",
 		"panic",
 		"panic_smp_self_stop",