diff --git a/module/zfs/vdev_queue.c b/module/zfs/vdev_queue.c
index e74df76b7530..86b20f134834 100644
--- a/module/zfs/vdev_queue.c
+++ b/module/zfs/vdev_queue.c
@@ -709,6 +709,18 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 	do {
 		dio = nio;
 		nio = AVL_NEXT(t, dio);
+		zio_add_child(dio, aio);
+		vdev_queue_io_remove(vq, dio);
+	} while (dio != last);
+
+	/*
+	 * We need to drop the vdev queue's lock during zio_execute() to
+	 * avoid a deadlock that we could encounter due to lock order
+	 * reversal between vq_lock and io_lock in zio_change_priority().
+	 * Use the dropped lock to do memory copy without congestion.
+	 */
+	mutex_exit(&vq->vq_lock);
+	while ((dio = zio_walk_parents(aio, &zl)) != NULL) {
 		ASSERT3U(dio->io_type, ==, aio->io_type);
 
 		if (dio->io_flags & ZIO_FLAG_NODATA) {
@@ -720,16 +732,6 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 			    dio->io_offset - aio->io_offset, 0, dio->io_size);
 		}
 
-		zio_add_child(dio, aio);
-		vdev_queue_io_remove(vq, dio);
-	} while (dio != last);
-
-	/*
-	 * We need to drop the vdev queue's lock to avoid a deadlock that we
-	 * could encounter since this I/O will complete immediately.
-	 */
-	mutex_exit(&vq->vq_lock);
-	while ((dio = zio_walk_parents(aio, &zl)) != NULL) {
 		zio_vdev_io_bypass(dio);
 		zio_execute(dio);
 	}