1 files changed, 34 insertions, 8 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 481951bf091d..087d18d771b5 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(&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 */
@@ -319,8 +325,14 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	task = create->result;
 	if (!IS_ERR(task)) {
 		static const struct sched_param param = { .sched_priority = 0 };
+		char name[TASK_COMM_LEN];
 
-		vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
+		/*
+		 * task is already visible to other tasks, so updating
+		 * COMM must be protected.
+		 */
+		vsnprintf(name, sizeof(name), namefmt, args);
+		set_task_comm(task, name);
 		/*
 		 * root may have changed our (kthreadd's) priority or CPU mask.
 		 * The kernel thread should not inherit these properties.
@@ -459,8 +471,10 @@ void kthread_unpark(struct task_struct *k)
 	if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
 		__kthread_bind(k, kthread->cpu, TASK_PARKED);
 
-	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);
@@ -484,10 +498,22 @@ int kthread_park(struct task_struct *k)
 	if (WARN_ON(k->flags & PF_EXITING))
 		return -ENOSYS;
 
+	if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
+		return -EBUSY;
+
 	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;