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Subject[055/139] x86: Fix double enable_IR_x2apic() call on SMP kernel on !SMP boards
2.6.33-stable review patch.  If anyone has any objections, please let us know.


From: Suresh Siddha <>

commit 472a474c6630efd195d3738339fd1bdc8aa3b1aa upstream.

Jan Grossmann reported kernel boot panic while booting SMP
kernel on his system with a single core cpu. SMP kernels call
enable_IR_x2apic() from native_smp_prepare_cpus() and on
platforms where the kernel doesn't find SMP configuration we
ended up again calling enable_IR_x2apic() from the
APIC_init_uniprocessor() call in the smp_sanity_check(). Thus
leading to kernel panic.

Don't call enable_IR_x2apic() and default_setup_apic_routing()
from APIC_init_uniprocessor() in CONFIG_SMP case.

NOTE: this kind of non-idempotent and assymetric initialization
sequence is rather fragile and unclean, we'll clean that up
in v2.6.35. This is the minimal fix for v2.6.34.

Signed-off-by: Suresh Siddha <>
Cc: <>
Cc: <>
Cc: <>
Cc: <>
Cc: <>
LKML-Reference: <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86/kernel/apic/apic.c | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1640,8 +1640,10 @@ int __init APIC_init_uniprocessor(void)

+#ifndef CONFIG_SMP


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