md/raid10: resize bitmap when required during reshape.

If a reshape changes the size of the array, then we can now
update the bitmap to suit - so do so.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid10.c

@@ -3786,8 +3786,6 @@ static int raid10_check_reshape(struct mddev *mddev)
 			/* not factor of array size */
 			return -EINVAL;
 
-	if (mddev->bitmap)
-		return -EBUSY;
 	if (!enough(conf, -1))
 		return -EINVAL;
 
@@ -3882,6 +3880,7 @@ static int raid10_start_reshape(struct mddev *mddev)
 	struct r10conf *conf = mddev->private;
 	struct md_rdev *rdev;
 	int spares = 0;
+	int ret;
 
 	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		return -EBUSY;
@@ -3943,6 +3942,14 @@ static int raid10_start_reshape(struct mddev *mddev)
 		conf->reshape_progress = 0;
 	spin_unlock_irq(&conf->device_lock);
 
+	if (mddev->delta_disks && mddev->bitmap) {
+		ret = bitmap_resize(mddev->bitmap,
+				    raid10_size(mddev, 0,
+						conf->geo.raid_disks),
+				    0, 0);
+		if (ret)
+			goto abort;
+	}
 	if (mddev->delta_disks > 0) {
 		rdev_for_each(rdev, mddev)
 			if (rdev->raid_disk < 0 &&
@@ -3982,6 +3989,15 @@ static int raid10_start_reshape(struct mddev *mddev)
 	mddev->sync_thread = md_register_thread(md_do_sync, mddev,
 						"reshape");
 	if (!mddev->sync_thread) {
+		ret = -EAGAIN;
+		goto abort;
+	}
+	conf->reshape_checkpoint = jiffies;
+	md_wakeup_thread(mddev->sync_thread);
+	md_new_event(mddev);
+	return 0;
+
+abort:
 	mddev->recovery = 0;
 	spin_lock_irq(&conf->device_lock);
 	conf->geo = conf->prev;
@@ -3992,12 +4008,7 @@ static int raid10_start_reshape(struct mddev *mddev)
 	conf->reshape_progress = MaxSector;
 	mddev->reshape_position = MaxSector;
 	spin_unlock_irq(&conf->device_lock);
-		return -EAGAIN;
-	}
-	conf->reshape_checkpoint = jiffies;
-	md_wakeup_thread(mddev->sync_thread);
-	md_new_event(mddev);
-	return 0;
+	return ret;
 }
 
 /* Calculate the last device-address that could contain