arm64/cpu: Mark cpu_park_loop() and friends __noreturn

In preparation for marking panic_smp_self_stop() __noreturn across the
kernel, first mark the arm64 implementation of cpu_park_loop() and
related functions __noreturn.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/55787d3193ea3e295ccbb097abfab0a10ae49d45.1681342859.git.jpoimboe@kernel.org

arch/arm64/include/asm/exception.h

@@ -31,7 +31,7 @@ static inline unsigned long disr_to_esr(u64 disr)
 	return esr;
 }
 
-asmlinkage void handle_bad_stack(struct pt_regs *regs);
+asmlinkage void __noreturn handle_bad_stack(struct pt_regs *regs);
 
 asmlinkage void el1t_64_sync_handler(struct pt_regs *regs);
 asmlinkage void el1t_64_irq_handler(struct pt_regs *regs);
@@ -80,5 +80,5 @@ void do_el1_fpac(struct pt_regs *regs, unsigned long esr);
 void do_serror(struct pt_regs *regs, unsigned long esr);
 void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags);
 
-void panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far);
+void __noreturn panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far);
 #endif	/* __ASM_EXCEPTION_H */

arch/arm64/include/asm/smp.h

@@ -101,9 +101,9 @@ extern int __cpu_disable(void);
 
 extern void __cpu_die(unsigned int cpu);
 extern void __noreturn cpu_die(void);
-extern void cpu_die_early(void);
+extern void __noreturn cpu_die_early(void);
 
-static inline void cpu_park_loop(void)
+static inline void __noreturn cpu_park_loop(void)
 {
 	for (;;) {
 		wfe();
@@ -123,7 +123,7 @@ static inline void update_cpu_boot_status(int val)
  * which calls for a kernel panic. Update the boot status and park the calling
  * CPU.
  */
-static inline void cpu_panic_kernel(void)
+static inline void __noreturn cpu_panic_kernel(void)
 {
 	update_cpu_boot_status(CPU_PANIC_KERNEL);
 	cpu_park_loop();

arch/arm64/kernel/entry-common.c

@@ -840,7 +840,7 @@ UNHANDLED(el0t, 32, error)
 #endif /* CONFIG_COMPAT */
 
 #ifdef CONFIG_VMAP_STACK
-asmlinkage void noinstr handle_bad_stack(struct pt_regs *regs)
+asmlinkage void noinstr __noreturn handle_bad_stack(struct pt_regs *regs)
 {
 	unsigned long esr = read_sysreg(esr_el1);
 	unsigned long far = read_sysreg(far_el1);

arch/arm64/kernel/smp.c

@@ -398,7 +398,7 @@ static void __cpu_try_die(int cpu)
  * Kill the calling secondary CPU, early in bringup before it is turned
  * online.
  */
-void cpu_die_early(void)
+void __noreturn cpu_die_early(void)
 {
 	int cpu = smp_processor_id();
 
@@ -816,7 +816,7 @@ void arch_irq_work_raise(void)
 }
 #endif
 
-static void local_cpu_stop(void)
+static void __noreturn local_cpu_stop(void)
 {
 	set_cpu_online(smp_processor_id(), false);
 
@@ -839,7 +839,7 @@ void panic_smp_self_stop(void)
 static atomic_t waiting_for_crash_ipi = ATOMIC_INIT(0);
 #endif
 
-static void ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs)
+static void __noreturn ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs)
 {
 #ifdef CONFIG_KEXEC_CORE
 	crash_save_cpu(regs, cpu);
@@ -854,6 +854,8 @@ static void ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs)
 
 	/* just in case */
 	cpu_park_loop();
+#else
+	BUG();
 #endif
 }
 

arch/arm64/kernel/traps.c

@@ -863,7 +863,7 @@ void bad_el0_sync(struct pt_regs *regs, int reason, unsigned long esr)
 DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
 	__aligned(16);
 
-void panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far)
+void __noreturn panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far)
 {
 	unsigned long tsk_stk = (unsigned long)current->stack;
 	unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr);
@@ -905,7 +905,6 @@ void __noreturn arm64_serror_panic(struct pt_regs *regs, unsigned long esr)
 	nmi_panic(regs, "Asynchronous SError Interrupt");
 
 	cpu_park_loop();
-	unreachable();
 }
 
 bool arm64_is_fatal_ras_serror(struct pt_regs *regs, unsigned long esr)