kernel: Add support for stopping workqueues

This patch adds support for stopping workqueues. This is useful for freeing
resources from workqueues when subsystems/modules is deactivated or
cleaning up the system between tests in ztest to reach a fully normalized
state.

The patch adds a new function k_work_queue_stop() that releases the
workqueues thread and stack when a workqueue is unwanted.
k_work_queue_stop(...) should be viewed as a counterpart to
k_work_queue_start(...).

This would allow to:
k_work_queue_start(...);

k_work_drain(..., true);
k_work_queue_stop(...);

Signed-off-by: Måns Ansgariusson <[email protected]>

include/zephyr/kernel.h

@@ -3606,6 +3606,19 @@ int k_work_queue_drain(struct k_work_q *queue, bool plug);
  */
 int k_work_queue_unplug(struct k_work_q *queue);
 
+/** @brief Stop a work queue.
+ *
+ * This stops the work queue thread and releases its resources. This should be
+ * invoked when the work queue is no longer needed.
+ *
+ * @param queue pointer to the queue structure.
+ *
+ * @retval 0 if the work queue was stopped
+ * @retval -ENODEV if the work queue was not started
+ * @retval -EBUSY if the work queue is actively processing work items
+ */
+int k_work_queue_stop(struct k_work_q *queue);
+
 /** @brief Initialize a delayable work structure.
  *
  * This must be invoked before scheduling a delayable work structure for the
@@ -3915,6 +3928,8 @@ enum {
 	K_WORK_QUEUE_DRAIN = BIT(K_WORK_QUEUE_DRAIN_BIT),
 	K_WORK_QUEUE_PLUGGED_BIT = 3,
 	K_WORK_QUEUE_PLUGGED = BIT(K_WORK_QUEUE_PLUGGED_BIT),
+	K_WORK_QUEUE_STOP_BIT = 4,
+	K_WORK_QUEUE_STOP = BIT(K_WORK_QUEUE_STOP_BIT),
 
 	/* Static work queue flags */
 	K_WORK_QUEUE_NO_YIELD_BIT = 8,

kernel/work.c

@@ -653,6 +653,12 @@ static void work_queue_main(void *workq_ptr, void *p2, void *p3)
 			 * submissions.
 			 */
 			(void)z_sched_wake_all(&queue->drainq, 1, NULL);
+		} else if (flag_test(&queue->flags, K_WORK_QUEUE_STOP_BIT)) {
+			/* User has requested that the queue stop. Clear the status flags and exit.
+			 */
+			flags_set(&queue->flags, 0);
+			k_spin_unlock(&lock, key);
+			return;
 		} else {
 			/* No work is available and no queue state requires
 			 * special handling.
@@ -812,6 +818,30 @@ int k_work_queue_unplug(struct k_work_q *queue)
 	return ret;
 }
 
+int k_work_queue_stop(struct k_work_q *queue)
+{
+	__ASSERT_NO_MSG(queue);
+
+	k_spinlock_key_t key = k_spin_lock(&lock);
+
+	if (!flag_test(&queue->flags, K_WORK_QUEUE_STARTED_BIT)) {
+		k_spin_unlock(&lock, key);
+		return -ENODEV;
+	}
+
+	if (!flag_test(&queue->flags, K_WORK_QUEUE_PLUGGED_BIT)) {
+		k_spin_unlock(&lock, key);
+		return -EBUSY;
+	}
+
+	flag_set(&queue->flags, K_WORK_QUEUE_STOP_BIT);
+	notify_queue_locked(queue);
+	k_spin_unlock(&lock, key);
+	k_thread_join(&queue->thread, K_FOREVER);
+
+	return 0;
+}
+
 #ifdef CONFIG_SYS_CLOCK_EXISTS
 
 /* Timeout handler for delayable work.