1 files changed, 24 insertions, 6 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 481951bf091d..750cb8082694 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -177,9 +177,20 @@ void *kthread_probe_data(struct task_struct *task)
 static void __kthread_parkme(struct kthread *self)
 {
         for (;;) {
-                set_current_state(TASK_PARKED);
+                /*
+                 * TASK_PARKED is a special state; we must serialize against
+                 * possible pending wakeups to avoid store-store collisions on
+                 * task->state.
+                 *
+                 * Such a collision might possibly result in the task state
+                 * changin from TASK_PARKED and us failing the
+                 * wait_task_inactive() in kthread_park().
+                 */
+                set_special_state(TASK_PARKED);
                 if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
                         break;
+
+                complete_all(&self->parked);
                 schedule();
         }
         __set_current_state(TASK_RUNNING);
@@ -191,11 +202,6 @@ void kthread_parkme(void)
 }
 EXPORT_SYMBOL_GPL(kthread_parkme);
 
-void kthread_park_complete(struct task_struct *k)
-{
-        complete_all(&to_kthread(k)->parked);
-}
-
 static int kthread(void *_create)
 {
         /* Copy data: it's on kthread's stack */
@@ -461,6 +467,9 @@ void kthread_unpark(struct task_struct *k)
 
         reinit_completion(&kthread->parked);
         clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+        /*
+         * __kthread_parkme() will either see !SHOULD_PARK or get the wakeup.
+         */
         wake_up_state(k, TASK_PARKED);
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
@@ -487,7 +496,16 @@ int kthread_park(struct task_struct *k)
         set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
         if (k != current) {
                 wake_up_process(k);
+                /*
+                 * Wait for __kthread_parkme() to complete(), this means we
+                 * _will_ have TASK_PARKED and are about to call schedule().
+                 */
                 wait_for_completion(&kthread->parked);
+                /*
+                 * Now wait for that schedule() to complete and the task to
+                 * get scheduled out.
+                 */
+                WARN_ON_ONCE(!wait_task_inactive(k, TASK_PARKED));
         }
 
         return 0;