1 files changed, 10 insertions, 0 deletions

diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index eba7f53f8b4a..7007e1783797 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;