1 files changed, 34 insertions, 6 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index d26d0b095b3b..2cc409ce0a8f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -64,6 +64,8 @@ void __init cpu_hotplug_init(void)
         cpu_hotplug.refcount = 0;
 }
 
+cpumask_t cpu_active_map;
+
 #ifdef CONFIG_HOTPLUG_CPU
 
 void get_online_cpus(void)
@@ -291,11 +293,30 @@ int __ref cpu_down(unsigned int cpu)
         int err = 0;
 
         cpu_maps_update_begin();
-        if (cpu_hotplug_disabled)
+
+        if (cpu_hotplug_disabled) {
                 err = -EBUSY;
-        else
-                err = _cpu_down(cpu, 0);
+                goto out;
+        }
+
+        cpu_clear(cpu, cpu_active_map);
+
+        /*
+         * Make sure the all cpus did the reschedule and are not
+         * using stale version of the cpu_active_map.
+         * This is not strictly necessary becuase stop_machine()
+         * that we run down the line already provides the required
+         * synchronization. But it's really a side effect and we do not
+         * want to depend on the innards of the stop_machine here.
+         */
+        synchronize_sched();
+
+        err = _cpu_down(cpu, 0);
 
+        if (cpu_online(cpu))
+                cpu_set(cpu, cpu_active_map);
+
+out:
         cpu_maps_update_done();
         return err;
 }
@@ -355,11 +376,18 @@ int __cpuinit cpu_up(unsigned int cpu)
         }
 
         cpu_maps_update_begin();
-        if (cpu_hotplug_disabled)
+
+        if (cpu_hotplug_disabled) {
                 err = -EBUSY;
-        else
-                err = _cpu_up(cpu, 0);
+                goto out;
+        }
+
+        err = _cpu_up(cpu, 0);
 
+        if (cpu_online(cpu))
+                cpu_set(cpu, cpu_active_map);
+
+out:
         cpu_maps_update_done();
         return err;
 }