[S390] smp: fix sigp stop handling

According to the architecture a cpu must not necessarily enter stopped
state after completion of a sigp instruction with "stop" order code.
So remove the BUG() statement after self sending sigp stop to avoid
that it ever gets reached.
Also add a sigp busy check to make sure that the order gets delivered.

Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/kernel/ipl.c

···
 {
 	if (strcmp(trigger->name, ON_PANIC_STR) == 0)
 		disabled_wait((unsigned long) __builtin_return_address(0));
-	else {
-		signal_processor(smp_processor_id(), sigp_stop);
-		for (;;);
-	}
+	while (signal_processor(smp_processor_id(), sigp_stop) == sigp_busy)
+		cpu_relax();
+	for (;;);
 }
 
 static struct shutdown_action stop_action = {SHUTDOWN_ACTION_STOP_STR,

arch/s390/kernel/smp.c

···
 void cpu_die(void)
 {
 	idle_task_exit();
-	signal_processor(smp_processor_id(), sigp_stop);
-	BUG();
+	while (signal_processor(smp_processor_id(), sigp_stop) == sigp_busy)
+		cpu_relax();
 	for (;;);
 }
 

arch/s390/kernel/swsusp_asm64.S

···
 	brc	2,4b			/* busy, try again */
 5:
 	sigp	%r9,%r2,__SIGP_STOP	/* stop resume (current) CPU */
+	brc	2,5b			/* busy, try again */
 6:	j	6b
 
 restart_suspend: