Disable the 8259A acting in the "virtual wire" mode to keep the interrupt
line inactive while fiddling with local APIC interrupt vector registers
associated with its destination inputs.  To be on the safe side, 
especially concerning flipping the trigger mode.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
---
patch-2.6.26-rc1-20080505-timer-8259-nmi-unmask-0
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_32.c linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_32.c
--- linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_32.c	2008-05-21 18:52:36.000000000 +0000
+++ linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_32.c	2008-05-21 18:52:36.000000000 +0000
@@ -2199,7 +2199,9 @@ static inline void __init check_timer(vo
 			else
 				add_pin_to_irq(0, apic2, pin2);
 			if (nmi_watchdog == NMI_IO_APIC) {
+				disable_8259A_irq(0);
 				setup_nmi();
+				enable_8259A_irq(0);
 			}
 			goto out;
 		}
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_64.c linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_64.c
--- linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_64.c	2008-05-21 19:00:05.000000000 +0000
+++ linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_64.c	2008-05-18 00:24:43.000000000 +0000
@@ -1702,7 +1702,9 @@ static inline void __init check_timer(vo
 			apic_printk(APIC_VERBOSE," works.\n");
 			nmi_watchdog_default();
 			if (nmi_watchdog == NMI_IO_APIC) {
+				disable_8259A_irq(0);
 				setup_nmi();
+				enable_8259A_irq(0);
 			}
 			goto out;
 		}
--
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