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

3 files changed, 26 insertions, 1 deletions

diff --git a/arch/s390/include/asm/s390_ext.h b/arch/s390/include/asm/s390_ext.h
index 080876d5f196..85b2154b899f 100644
--- a/arch/s390/include/asm/s390_ext.h
+++ b/arch/s390/include/asm/s390_ext.h
@@ -13,5 +13,7 @@ typedef void (*ext_int_handler_t)(unsigned int, unsigned int, unsigned long);
 
 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 */
diff --git a/arch/s390/kernel/s390_ext.c b/arch/s390/kernel/s390_ext.c
index 185029919c4d..87b5c532abf1 100644
--- a/arch/s390/kernel/s390_ext.c
+++ b/arch/s390/kernel/s390_ext.c
@@ -106,3 +106,26 @@ void __irq_entry do_extint(struct pt_regs *regs, unsigned int ext_int_code,
         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);
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index e46ba2927424..6e922b50efa4 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -613,7 +613,7 @@ static int __init pfault_irq_init(void)
         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;