+/*
+ * btrfs_start_workers uses kthread_run, which can block waiting for memory
+ * for a very long time. It will actually throttle on page writeback,
+ * and so it may not make progress until after our btrfs worker threads
+ * process all of the pending work structs in their queue
+ *
+ * This means we can't use btrfs_start_workers from inside a btrfs worker
+ * thread that is used as part of cleaning dirty memory, which pretty much
+ * involves all of the worker threads.
+ *
+ * Instead we have a helper queue who never has more than one thread
+ * where we scheduler thread start operations. This worker_start struct
+ * is used to contain the work and hold a pointer to the queue that needs
+ * another worker.
+ */
+struct worker_start {
+ struct btrfs_work work;
+ struct btrfs_workers *queue;
+};
+
+static void start_new_worker_func(struct btrfs_work *work)
+{
+ struct worker_start *start;
+ start = container_of(work, struct worker_start, work);
+ btrfs_start_workers(start->queue, 1);
+ kfree(start);
+}
+
+static int start_new_worker(struct btrfs_workers *queue)
+{
+ struct worker_start *start;
+ int ret;
+
+ start = kzalloc(sizeof(*start), GFP_NOFS);
+ if (!start)
+ return -ENOMEM;
+
+ start->work.func = start_new_worker_func;
+ start->queue = queue;
+ ret = btrfs_queue_worker(queue->atomic_worker_start, &start->work);
+ if (ret)
+ kfree(start);
+ return ret;
+}
+