x86: enable NMI watchdog on nosmp

if nosmp has been passed as a boot option, but nmi_watchdog=2 has also
been enabled then keep minimal local APIC functionality around to make
the watchdog work.

this allowed me to debug a hard hang that would only occur with a nosmp
bootup.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kernel/smpboot_32.c b/arch/x86/kernel/smpboot_32.c
index edc9db69a118..83e4f40f8dc9 100644
--- a/arch/x86/kernel/smpboot_32.c
+++ b/arch/x86/kernel/smpboot_32.c
@@ -1021,6 +1021,12 @@ static void __init smp_boot_cpus(unsigned int max_cpus)
         if (!max_cpus) {
                 smp_found_config = 0;
                 printk(KERN_INFO "SMP mode deactivated, forcing use of dummy APIC emulation.\n");
+
+                if (nmi_watchdog == NMI_LOCAL_APIC) {
+                        printk(KERN_INFO "activating minimal APIC for NMI watchdog use.\n");
+                        connect_bsp_APIC();
+                        setup_local_APIC();
+                }
                 smpboot_clear_io_apic_irqs();
                 phys_cpu_present_map = physid_mask_of_physid(0);
                 cpu_set(0, per_cpu(cpu_sibling_map, 0));