1 files changed, 21 insertions, 5 deletions

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 912823e2a11b..22d1d77f9a62 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -40,6 +40,8 @@ static atomic_t thread_ack;
 static DEFINE_MUTEX(lock);
 /* setup_lock protects refcount, stop_machine_wq and stop_machine_work. */
 static DEFINE_MUTEX(setup_lock);
+/* do not start up until all worklets have been placed: */
+static DEFINE_MUTEX(startup_lock);
 /* Users of stop_machine. */
 static int refcount;
 static struct workqueue_struct *stop_machine_wq;
@@ -71,6 +73,15 @@ static void stop_cpu(struct work_struct *unused)
         int cpu = smp_processor_id();
         int err;
 
+        /*
+         * Wait for the startup loop to finish:
+         */
+        mutex_lock(&startup_lock);
+        /*
+         * Let other threads continue too:
+         */
+        mutex_unlock(&startup_lock);
+
         if (!active_cpus) {
                 if (cpu == cpumask_first(cpu_online_mask))
                         smdata = &active;
@@ -166,16 +177,21 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 
         set_state(STOPMACHINE_PREPARE);
 
-        /* Schedule the stop_cpu work on all cpus: hold this CPU so one
-         * doesn't hit this CPU until we're ready. */
-        get_cpu();
+        /*
+         * Schedule the stop_cpu work on all cpus before allowing any
+         * of the CPUs to execute it:
+         */
+        mutex_lock(&startup_lock);
+
         for_each_online_cpu(i) {
                 sm_work = per_cpu_ptr(stop_machine_work, i);
                 INIT_WORK(sm_work, stop_cpu);
                 queue_work_on(i, stop_machine_wq, sm_work);
         }
-        /* This will release the thread on our CPU. */
-        put_cpu();
+
+        /* This will release the thread on all CPUs: */
+        mutex_unlock(&startup_lock);
+
         flush_workqueue(stop_machine_wq);
         ret = active.fnret;
         mutex_unlock(&lock);