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-rw-r--r--arch/i386/kernel/smpboot.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index eba7f53f8b4..7007e178379 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -1029,6 +1029,16 @@ int __devinit smp_prepare_cpu(int cpu)
int apicid, ret;
lock_cpu_hotplug();
+
+ /*
+ * On x86, CPU0 is never offlined. Trying to bring up an
+ * already-booted CPU will hang. So check for that case.
+ */
+ if (cpu_online(cpu)) {
+ ret = -EINVAL;
+ goto exit;
+ }
+
apicid = x86_cpu_to_apicid[cpu];
if (apicid == BAD_APICID) {
ret = -ENODEV;