Index: ksrc/arch/powerpc/hal.c
===================================================================
--- ksrc/arch/powerpc/hal.c	(revision 3095)
+++ ksrc/arch/powerpc/hal.c	(working copy)
@@ -245,6 +245,11 @@
 
     rthal_irq_desc_status(irq) &= ~IRQ_DISABLED;
 
+    if (rthal_irq_handlerp(irq)->unmask == NULL) {
+      printk("NULL ->unmask handler, IRQ %d, chip %s\n", irq, rthal_irq_handlerp(irq)->typename);
+      return 0;
+    }
+
     return rthal_irq_chip_enable(irq);
 }