[PATCH] x86_64: Restore the proper NR_IRQS define so larger systems work.

[Eric W. Biederman]

As pointed out and tracked by Yinghai Lu <yhlu.kernel@xxxxxxxxx>:

Dhaval Giani got:
kernel BUG at arch/x86/kernel/io_apic_64.c:357!
invalid opcode: 0000 [1] SMP
CPU 24
...

his system (x3950) has 8 ioapic, irq > 256

This was caused by:
        commit 9b7dc567d03d74a1fbae84e88949b6a60d922d82
        Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
        Date:   Fri May 2 20:10:09 2008 +0200

           x86: unify interrupt vector defines

           The interrupt vector defines are copied 4 times around with minimal
           differences. Move them all into asm-x86/irq_vectors.h

It appears that Thomas did not notice that x86_64 does something
completely different when he merge irq_vectors.h

We can solve this for 2.6.27 by simply reintroducing the old heuristic
for setting NR_IRQS on x86_64 to a usable value, which trivially removes
the regression.

Long term it would be nice to harmonize the handling of ioapic interrupts
of x86_32 and x86_64 so we don't have this kind of confusion.

Dhaval Giani <dhaval@xxxxxxxxxxxxxxxxxx> tested an earlier version of
this patch by YH which confirms simply increasing NR_IRQS fixes the
problem.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
---
 include/asm-x86/irq_vectors.h |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/include/asm-x86/irq_vectors.h b/include/asm-x86/irq_vectors.h
index 90b1d1f..a13eb6c 100644
--- a/include/asm-x86/irq_vectors.h
+++ b/include/asm-x86/irq_vectors.h
@@ -109,7 +109,15 @@
 #define LAST_VM86_IRQ		15
 #define invalid_vm86_irq(irq)	((irq) < 3 || (irq) > 15)
 
-#if !defined(CONFIG_X86_VOYAGER)
+#ifdef CONFIG_X86_64
+# if NR_CPUS < MAX_IO_APICS
+#  define NR_IRQS (NR_VECTORS + (32 * NR_CPUS))
+# else
+#  define NR_IRQS (NR_VECTORS + (32 * MAX_IO_APICS ))
+# endif
+# define NR_IRQ_VECTORS NR_IRQS
+
+#elif !defined(CONFIG_X86_VOYAGER)
 
 # if defined(CONFIG_X86_IO_APIC) || defined(CONFIG_PARAVIRT) || defined(CONFIG_X86_VISWS)
 
-- 
1.5.3.rc6.17.g1911
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