[PATCH v2] x86: Don't allow nr_irqs > NR_IRQS

[Ben Hutchings <bhutchings@solarflare.com>]

On some systems probe_nr_irqs() can return a value larger than
NR_IRQS.  This will lead to probe_irq_on() overrunning the irq_desc
array.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
---
 arch/x86/kernel/io_apic.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

I hit this when running net-next-2.6 (close to 2.6.28-rc3) on a
Supermicro dual Xeon system.  NR_IRQS is 224 but probe_nr_irqs() detects
5 IOAPICs and returns 240.  Here are the log messages:

Tue Nov  4 16:53:47 2008 ACPI: IOAPIC (id[0x01] address[0xfec00000] gsi_base[0])
Tue Nov  4 16:53:47 2008 IOAPIC[0]: apic_id 1, version 32, address 0xfec00000, GSI 0-23
Tue Nov  4 16:53:47 2008 ACPI: IOAPIC (id[0x02] address[0xfec81000] gsi_base[24])
Tue Nov  4 16:53:47 2008 IOAPIC[1]: apic_id 2, version 32, address 0xfec81000, GSI 24-47
Tue Nov  4 16:53:47 2008 ACPI: IOAPIC (id[0x03] address[0xfec81400] gsi_base[48])
Tue Nov  4 16:53:47 2008 IOAPIC[2]: apic_id 3, version 32, address 0xfec81400, GSI 48-71
Tue Nov  4 16:53:47 2008 ACPI: IOAPIC (id[0x04] address[0xfec82000] gsi_base[72])
Tue Nov  4 16:53:47 2008 IOAPIC[3]: apic_id 4, version 32, address 0xfec82000, GSI 72-95
Tue Nov  4 16:53:47 2008 ACPI: IOAPIC (id[0x05] address[0xfec82400] gsi_base[96])
Tue Nov  4 16:53:47 2008 IOAPIC[4]: apic_id 5, version 32, address 0xfec82400, GSI 96-119
Tue Nov  4 16:53:47 2008 ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 high edge)
Tue Nov  4 16:53:47 2008 ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level)
Tue Nov  4 16:53:47 2008 Enabling APIC mode:  Flat.  Using 5 I/O APICs

I have added a WARN_ON() as suggested by Yinghai Lu.

Ben.

diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
--- a/arch/x86/kernel/io_apic.c
+++ b/arch/x86/kernel/io_apic.c
@@ -3611,6 +3611,8 @@ int __init probe_nr_irqs(void)
 	/* something wrong ? */
 	if (nr < nr_min)
 		nr = nr_min;
+	if (WARN_ON(nr > NR_IRQS))
+		nr = NR_IRQS;
 
 	return nr;
 }

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.