cpu: Mark nmi_panic_self_stop() __noreturn

In preparation for improving objtool's handling of weak noreturn
functions, mark nmi_panic_self_stop() __noreturn.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/316fc6dfab5a8c4e024c7185484a1ee5fb0afb79.1681342859.git.jpoimboe@kernel.org

arch/x86/include/asm/reboot.h

@@ -28,7 +28,6 @@ void __noreturn machine_real_restart(unsigned int type);
 void cpu_emergency_disable_virtualization(void);
 
 typedef void (*nmi_shootdown_cb)(int, struct pt_regs*);
-void nmi_panic_self_stop(struct pt_regs *regs);
 void nmi_shootdown_cpus(nmi_shootdown_cb callback);
 void run_crash_ipi_callback(struct pt_regs *regs);
 

arch/x86/kernel/reboot.c

@@ -920,7 +920,7 @@ void run_crash_ipi_callback(struct pt_regs *regs)
 }
 
 /* Override the weak function in kernel/panic.c */
-void nmi_panic_self_stop(struct pt_regs *regs)
+void __noreturn nmi_panic_self_stop(struct pt_regs *regs)
 {
 	while (1) {
 		/* If no CPU is preparing crash dump, we simply loop here. */

include/linux/smp.h

@@ -60,7 +60,7 @@ int smp_call_function_single_async(int cpu, struct __call_single_data *csd);
  * Architecture-dependent code may override them.
  */
 void __noreturn panic_smp_self_stop(void);
-void nmi_panic_self_stop(struct pt_regs *regs);
+void __noreturn nmi_panic_self_stop(struct pt_regs *regs);
 void crash_smp_send_stop(void);
 
 /*

kernel/panic.c

@@ -151,7 +151,7 @@ void __weak __noreturn panic_smp_self_stop(void)
  * Stop ourselves in NMI context if another CPU has already panicked. Arch code
  * may override this to prepare for crash dumping, e.g. save regs info.
  */
-void __weak nmi_panic_self_stop(struct pt_regs *regs)
+void __weak __noreturn nmi_panic_self_stop(struct pt_regs *regs)
 {
 	panic_smp_self_stop();
 }

tools/objtool/check.c

@@ -217,6 +217,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"lbug_with_loc",
 		"machine_real_restart",
 		"make_task_dead",
+		"nmi_panic_self_stop",
 		"panic",
 		"panic_smp_self_stop",
 		"rest_init",