md/raid5: export is_congested test

the dm module will need this for dm-raid45.

Also only access ->queue->backing_dev_info->congested_fn
if ->queue actually exists.  It won't in a dm target.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 9c462f6..ad6694f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3678,17 +3678,14 @@
 	unplug_slaves(mddev);
 }
 
-static int raid5_congested(void *data, int bits)
+int md_raid5_congested(mddev_t *mddev, int bits)
 {
-	mddev_t *mddev = data;
 	raid5_conf_t *conf = mddev->private;
 
 	/* No difference between reads and writes.  Just check
 	 * how busy the stripe_cache is
 	 */
 
-	if (mddev_congested(mddev, bits))
-		return 1;
 	if (conf->inactive_blocked)
 		return 1;
 	if (conf->quiesce)
@@ -3698,6 +3695,15 @@
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(md_raid5_congested);
+
+static int raid5_congested(void *data, int bits)
+{
+	mddev_t *mddev = data;
+
+	return mddev_congested(mddev, bits) ||
+		md_raid5_congested(mddev, bits);
+}
 
 /* We want read requests to align with chunks where possible,
  * but write requests don't need to.
@@ -5184,13 +5190,14 @@
 			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
 
 		blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);
+
+		mddev->queue->backing_dev_info.congested_data = mddev;
+		mddev->queue->backing_dev_info.congested_fn = raid5_congested;
 	}
 
 	mddev->queue->queue_lock = &conf->device_lock;
 
 	mddev->queue->unplug_fn = raid5_unplug_device;
-	mddev->queue->backing_dev_info.congested_data = mddev;
-	mddev->queue->backing_dev_info.congested_fn = raid5_congested;
 
 	chunk_size = mddev->chunk_sectors << 9;
 	blk_queue_io_min(mddev->queue, chunk_size);
@@ -5220,7 +5227,8 @@
 
 	md_unregister_thread(mddev->thread);
 	mddev->thread = NULL;
-	mddev->queue->backing_dev_info.congested_fn = NULL;
+	if (mddev->queue)
+		mddev->queue->backing_dev_info.congested_fn = NULL;
 	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
 	free_conf(conf);
 	mddev->private = NULL;
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 61b6b25..d6470de 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -497,5 +497,7 @@
 {
 	return layout >= 8 && layout <= 10;
 }
+
+extern int md_raid5_congested(mddev_t *mddev, int bits);
 extern int raid5_set_cache_size(mddev_t *mddev, int size);
 #endif