1 files changed, 101 insertions, 3 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 850b255649a2..d9b0be5c6a5f 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -65,7 +65,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
 static struct kthread *to_live_kthread(struct task_struct *k)
 {
 	struct completion *vfork = ACCESS_ONCE(k->vfork_done);
-	if (likely(vfork))
+	if (likely(vfork) && try_get_task_stack(k))
 		return __to_kthread(vfork);
 	return NULL;
 }
@@ -427,8 +427,10 @@ void kthread_unpark(struct task_struct *k)
 {
 	struct kthread *kthread = to_live_kthread(k);
 
-	if (kthread)
+	if (kthread) {
 		__kthread_unpark(k, kthread);
+		put_task_stack(k);
+	}
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
 
@@ -457,6 +459,7 @@ int kthread_park(struct task_struct *k)
 				wait_for_completion(&kthread->parked);
 			}
 		}
+		put_task_stack(k);
 		ret = 0;
 	}
 	return ret;
@@ -492,6 +495,7 @@ int kthread_stop(struct task_struct *k)
 		__kthread_unpark(k, kthread);
 		wake_up_process(k);
 		wait_for_completion(&kthread->exited);
+		put_task_stack(k);
 	}
 	ret = k->exit_code;
 	put_task_struct(k);
@@ -604,6 +608,19 @@ repeat:
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
+/*
+ * Returns true when the work could not be queued at the moment.
+ * It happens when it is already pending in a worker list
+ * or when it is being cancelled.
+ */
+static inline bool queuing_blocked(struct kthread_worker *worker,
+				   struct kthread_work *work)
+{
+	lockdep_assert_held(&worker->lock);
+
+	return !list_empty(&work->node) || work->canceling;
+}
+
 /* insert @work before @pos in @worker */
 static void insert_kthread_work(struct kthread_worker *worker,
 			       struct kthread_work *work,
@@ -633,7 +650,7 @@ bool queue_kthread_work(struct kthread_worker *worker,
 	unsigned long flags;
 
 	spin_lock_irqsave(&worker->lock, flags);
-	if (list_empty(&work->node)) {
+	if (!queuing_blocked(worker, work)) {
 		insert_kthread_work(worker, work, &worker->work_list);
 		ret = true;
 	}
@@ -694,6 +711,87 @@ retry:
 }
 EXPORT_SYMBOL_GPL(flush_kthread_work);
 
+/*
+ * This function removes the work from the worker queue. Also it makes sure
+ * that it won't get queued later via the delayed work's timer.
+ *
+ * The work might still be in use when this function finishes. See the
+ * current_work proceed by the worker.
+ *
+ * Return: %true if @work was pending and successfully canceled,
+ *	%false if @work was not pending
+ */
+static bool __kthread_cancel_work(struct kthread_work *work,
+				  unsigned long *flags)
+{
+	/*
+	 * Try to remove the work from a worker list. It might either
+	 * be from worker->work_list or from worker->delayed_work_list.
+	 */
+	if (!list_empty(&work->node)) {
+		list_del_init(&work->node);
+		return true;
+	}
+
+	return false;
+}
+
+static bool __kthread_cancel_work_sync(struct kthread_work *work)
+{
+	struct kthread_worker *worker = work->worker;
+	unsigned long flags;
+	int ret = false;
+
+	if (!worker)
+		goto out;
+
+	spin_lock_irqsave(&worker->lock, flags);
+	/* Work must not be used with >1 worker, see kthread_queue_work(). */
+	WARN_ON_ONCE(work->worker != worker);
+
+	ret = __kthread_cancel_work(work, &flags);
+
+	if (worker->current_work != work)
+		goto out_fast;
+
+	/*
+	 * The work is in progress and we need to wait with the lock released.
+	 * In the meantime, block any queuing by setting the canceling counter.
+	 */
+	work->canceling++;
+	spin_unlock_irqrestore(&worker->lock, flags);
+	flush_kthread_work(work);
+	spin_lock_irqsave(&worker->lock, flags);
+	work->canceling--;
+
+out_fast:
+	spin_unlock_irqrestore(&worker->lock, flags);
+out:
+	return ret;
+}
+
+/**
+ * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
+ * @work: the kthread work to cancel
+ *
+ * Cancel @work and wait for its execution to finish.  This function
+ * can be used even if the work re-queues itself. On return from this
+ * function, @work is guaranteed to be not pending or executing on any CPU.
+ *
+ * kthread_cancel_work_sync(&delayed_work->work) must not be used for
+ * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
+ *
+ * The caller must ensure that the worker on which @work was last
+ * queued can't be destroyed before this function returns.
+ *
+ * Return: %true if @work was pending, %false otherwise.
+ */
+bool kthread_cancel_work_sync(struct kthread_work *work)
+{
+	return __kthread_cancel_work_sync(work);
+}
+EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
+
 /**
  * flush_kthread_worker - flush all current works on a kthread_worker
  * @worker: worker to flush