[S390] outstanding interrupts vs. smp_send_stop

The panic function will first print the panic message to the console,
then stop additional cpus with smp_send_stop and finally call the
function on the panic notifier list.
In case of an I/O based console the panic message will cause I/O to
be started and a function on the panic notifier list will wait for the
completion of the I/O. That does not work if an I/O completion interrupt
has already been delivered to a cpu that is then stopped by smp_send_stop.
To break this cyclic dependency add code to smp_send_stop that gives
the additional cpu the opportunity to complete outstanding interrupts.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/sigp.h

@@ -56,6 +56,7 @@ enum {
 	ec_schedule = 0,
 	ec_call_function,
 	ec_call_function_single,
+	ec_stop_cpu,
 };
 
 /*