[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,
 };
 
 /*

arch/s390/kernel/smp.c

@@ -154,22 +154,52 @@ void smp_switch_to_ipl_cpu(void (*func)(void *), void *data)
 	smp_switch_to_cpu(func, data, sp, stap(), __cpu_logical_map[0]);
 }
 
+static void smp_stop_cpu(void)
+{
+	while (sigp(smp_processor_id(), sigp_stop) == sigp_busy)
+		cpu_relax();
+}
+
 void smp_send_stop(void)
 {
-	int cpu, rc;
+	cpumask_t cpumask;
+	int cpu;
+	u64 end;
 
 	/* Disable all interrupts/machine checks */
 	__load_psw_mask(psw_kernel_bits | PSW_MASK_DAT);
 	trace_hardirqs_off();
 
-	/* stop all processors */
-	for_each_online_cpu(cpu) {
-		if (cpu == smp_processor_id())
-			continue;
-		do {
-			rc = sigp(cpu, sigp_stop);
-		} while (rc == sigp_busy);
+	cpumask_copy(&cpumask, cpu_online_mask);
+	cpumask_clear_cpu(smp_processor_id(), &cpumask);
+
+	if (oops_in_progress) {
+		/*
+		 * Give the other cpus the opportunity to complete
+		 * outstanding interrupts before stopping them.
+		 */
+		end = get_clock() + (1000000UL << 12);
+		for_each_cpu(cpu, &cpumask) {
+			set_bit(ec_stop_cpu, (unsigned long *)
+				&lowcore_ptr[cpu]->ext_call_fast);
+			while (sigp(cpu, sigp_emergency_signal) == sigp_busy &&
+			       get_clock() < end)
+				cpu_relax();
+		}
+		while (get_clock() < end) {
+			for_each_cpu(cpu, &cpumask)
+				if (cpu_stopped(cpu))
+					cpumask_clear_cpu(cpu, &cpumask);
+			if (cpumask_empty(&cpumask))
+				break;
+			cpu_relax();
+		}
+	}
 
+	/* stop all processors */
+	for_each_cpu(cpu, &cpumask) {
+		while (sigp(cpu, sigp_stop) == sigp_busy)
+			cpu_relax();
 		while (!cpu_stopped(cpu))
 			cpu_relax();
 	}
@@ -194,6 +224,9 @@ static void do_ext_call_interrupt(unsigned int ext_int_code,
 	 */
 	bits = xchg(&S390_lowcore.ext_call_fast, 0);
 
+	if (test_bit(ec_stop_cpu, &bits))
+		smp_stop_cpu();
+
 	if (test_bit(ec_schedule, &bits))
 		scheduler_ipi();
 
@@ -202,6 +235,7 @@ static void do_ext_call_interrupt(unsigned int ext_int_code,
 
 	if (test_bit(ec_call_function_single, &bits))
 		generic_smp_call_function_single_interrupt();
+
 }
 
 /*