x86, io-apic: fix nmi_watchdog=1 bootup hang

nmi_watchdog=1 hangs on 64-bit:

[    0.250000] Detected 12.564 MHz APIC timer.
[    0.254178] APIC timer registered as dummy, due to nmi_watchdog=1!
[    0.260366] Testing NMI watchdog ... <4>WARNING: CPU#0: NMI appears to be stuck (0->0)!
[    ...     ]
[    0.470003] calling  genl_init+0x0/0xd0
[  hard hang ]

bisected it down to:

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| 317e1f2597ffb4d4db940577bbe56dc6e881ef07 is first bad commit
| commit 317e1f2597ffb4d4db940577bbe56dc6e881ef07
| Author: Maciej W. Rozycki <macro@linux-mips.org>
| Date:   Wed May 21 22:10:22 2008 +0100
|     x86: I/O APIC: clean up the 8259A on a NMI watchdog failure

the problem is that in the dummy-lapic branch we rely on the i8259A
but if the NMI watchdog fails we turn off IRQ 0 - which doesnt work
too well ;-)

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/x86/kernel/apic_64.c b/arch/x86/kernel/apic_64.c
index 07fda23a9f76..6cbc668a4c63 100644
--- a/arch/x86/kernel/apic_64.c
+++ b/arch/x86/kernel/apic_64.c
@@ -413,11 +413,13 @@ void __init setup_boot_APIC_clock(void)
          * PIT/HPET going.  Otherwise register lapic as a dummy
          * device.
          */
-        if (nmi_watchdog != NMI_IO_APIC)
+        if (nmi_watchdog != NMI_IO_APIC) {
                 lapic_clockevent.features &= ~CLOCK_EVT_FEAT_DUMMY;
-        else
+        } else {
                 printk(KERN_WARNING "APIC timer registered as dummy,"
                        " due to nmi_watchdog=1!\n");
+                timer_through_8259 = 1;
+        }
 
         setup_APIC_timer();
 }