[S390] irq: fix service signal external interrupt handling

Interrupt sources like pfault, sclp, dasd_diag and virtio all use the
service signal external interrupt subclass mask in control register 0
to enable and disable the corresponding interrupt.
Because no reference counting is implemented each subsystem thinks it
is the only user of subclass and sets and clears the bit like it wants.
This leads to case that unloading the dasd diag module under z/VM
causes both sclp and pfault interrupts to be masked. The result will
be locked up system sooner or later.
Fix this by introducing a new way to set (register) and clear
(unregister) the service signal subclass mask bit in cr0.
Also convert all drivers.

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

arch/s390/include/asm/s390_ext.h

···
 
 int register_external_interrupt(__u16 code, ext_int_handler_t handler);
 int unregister_external_interrupt(__u16 code, ext_int_handler_t handler);
+void service_subclass_irq_register(void);
+void service_subclass_irq_unregister(void);
 
 #endif /* _S390_EXTINT_H */

arch/s390/kernel/s390_ext.c

···
 	irq_exit();
 	set_irq_regs(old_regs);
 }
+
+static DEFINE_SPINLOCK(sc_irq_lock);
+static int sc_irq_refcount;
+
+void service_subclass_irq_register(void)
+{
+	spin_lock(&sc_irq_lock);
+	if (!sc_irq_refcount)
+		ctl_set_bit(0, 9);
+	sc_irq_refcount++;
+	spin_unlock(&sc_irq_lock);
+}
+EXPORT_SYMBOL(service_subclass_irq_register);
+
+void service_subclass_irq_unregister(void)
+{
+	spin_lock(&sc_irq_lock);
+	sc_irq_refcount--;
+	if (!sc_irq_refcount)
+		ctl_clear_bit(0, 9);
+	spin_unlock(&sc_irq_lock);
+}
+EXPORT_SYMBOL(service_subclass_irq_unregister);

arch/s390/mm/fault.c

···
 	rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
 	if (rc)
 		goto out_pfault;
-	ctl_set_bit(0, 9);
+	service_subclass_irq_register();
 	hotcpu_notifier(pfault_cpu_notify, 0);
 	return 0;
 

drivers/s390/block/dasd_diag.c

···
 	}
 	ASCEBC(dasd_diag_discipline.ebcname, 4);
 
-	ctl_set_bit(0, 9);
+	service_subclass_irq_register();
 	register_external_interrupt(0x2603, dasd_ext_handler);
 	dasd_diag_discipline_pointer = &dasd_diag_discipline;
 	return 0;
···
 dasd_diag_cleanup(void)
 {
 	unregister_external_interrupt(0x2603, dasd_ext_handler);
-	ctl_clear_bit(0, 9);
+	service_subclass_irq_unregister();
 	dasd_diag_discipline_pointer = NULL;
 }
 

drivers/s390/char/sclp.c

···
 		spin_unlock_irqrestore(&sclp_lock, flags);
 		/* Enable service-signal interruption - needs to happen
 		 * with IRQs enabled. */
-		ctl_set_bit(0, 9);
+		service_subclass_irq_register();
 		/* Wait for signal from interrupt or timeout */
 		sclp_sync_wait();
 		/* Disable service-signal interruption - needs to happen
 		 * with IRQs enabled. */
-		ctl_clear_bit(0,9);
+		service_subclass_irq_unregister();
 		spin_lock_irqsave(&sclp_lock, flags);
 		del_timer(&sclp_request_timer);
 		if (sclp_init_req.status == SCLP_REQ_DONE &&
···
 	spin_unlock_irqrestore(&sclp_lock, flags);
 	/* Enable service-signal external interruption - needs to happen with
 	 * IRQs enabled. */
-	ctl_set_bit(0, 9);
+	service_subclass_irq_register();
 	sclp_init_mask(1);
 	return 0;
 

drivers/s390/kvm/kvm_virtio.c

···
 
 	INIT_WORK(&hotplug_work, hotplug_devices);
 
-	ctl_set_bit(0, 9);
+	service_subclass_irq_register();
 	register_external_interrupt(0x2603, kvm_extint_handler);
 
 	scan_devices();