io-wq: make the io_wq ref counted

to #26323588

commit 848f7e1887c46f21679c2c12b9e8022f17750721 upstream.

In preparation for sharing an io-wq across different users, add a
reference count that manages destruction of it.
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io-wq.c

@@ -114,6 +114,8 @@ struct io_wq {
 	struct mm_struct *mm;
 	refcount_t refs;
 	struct completion done;
+
+	refcount_t use_refs;
 };
 
 static bool io_worker_get(struct io_worker *worker)
@@ -1074,6 +1076,7 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 			ret = -ENOMEM;
 			goto err;
 		}
+		refcount_set(&wq->use_refs, 1);
 		reinit_completion(&wq->done);
 		return wq;
 	}
@@ -1094,7 +1097,7 @@ static bool io_wq_worker_wake(struct io_worker *worker, void *data)
 	return false;
 }
 
-void io_wq_destroy(struct io_wq *wq)
+static void __io_wq_destroy(struct io_wq *wq)
 {
 	int node;
 
@@ -1114,3 +1117,9 @@ void io_wq_destroy(struct io_wq *wq)
 	kfree(wq->wqes);
 	kfree(wq);
 }
+
+void io_wq_destroy(struct io_wq *wq)
+{
+	if (refcount_dec_and_test(&wq->use_refs))
+		__io_wq_destroy(wq);
+}