diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 1023c4e48a91..76eed592371e 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3725,6 +3725,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 	int i;
 	int dd_idx;
 	sector_t writepos, safepos, gap;
+	sector_t stripe_addr;
 
 	if (sector_nr == 0) {
 		/* If restarting in the middle, skip the initial sectors */
@@ -3782,10 +3783,21 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 		wake_up(&conf->wait_for_overlap);
 	}
 
+	if (mddev->delta_disks < 0) {
+		BUG_ON(conf->reshape_progress == 0);
+		stripe_addr = writepos;
+		BUG_ON((mddev->dev_sectors &
+			~((sector_t)mddev->chunk_size / 512 - 1))
+		       - (conf->chunk_size / 512) - stripe_addr
+		       != sector_nr);
+	} else {
+		BUG_ON(writepos != sector_nr + conf->chunk_size / 512);
+		stripe_addr = sector_nr;
+	}
 	for (i=0; i < conf->chunk_size/512; i+= STRIPE_SECTORS) {
 		int j;
 		int skipped = 0;
-		sh = get_active_stripe(conf, sector_nr+i, 0, 0);
+		sh = get_active_stripe(conf, stripe_addr+i, 0, 0);
 		set_bit(STRIPE_EXPANDING, &sh->state);
 		atomic_inc(&conf->reshape_stripes);
 		/* If any of this stripe is beyond the end of the old
@@ -3825,10 +3837,10 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 	 * block on the destination stripes.
 	 */
 	first_sector =
-		raid5_compute_sector(conf, sector_nr*(new_data_disks),
+		raid5_compute_sector(conf, stripe_addr*(new_data_disks),
 				     1, &dd_idx, NULL);
 	last_sector =
-		raid5_compute_sector(conf, ((sector_nr+conf->chunk_size/512)
+		raid5_compute_sector(conf, ((stripe_addr+conf->chunk_size/512)
 					    *(new_data_disks) - 1),
 				     1, &dd_idx, NULL);
 	if (last_sector >= mddev->dev_sectors)
@@ -4366,12 +4378,6 @@ static int run(mddev_t *mddev)
 			       mdname(mddev));
 			return -EINVAL;
 		}
-		if (mddev->delta_disks <= 0) {
-			printk(KERN_ERR "raid5: %s: unsupported reshape "
-			       "(reduce disks) required - aborting.\n",
-			       mdname(mddev));
-			return -EINVAL;
-		}
 		old_disks = mddev->raid_disks - mddev->delta_disks;
 		/* reshape_position must be on a new-stripe boundary, and one
 		 * further up in new geometry must map after here in old
@@ -4648,6 +4654,10 @@ static int raid5_remove_disk(mddev_t *mddev, int number)
 	print_raid5_conf(conf);
 	rdev = p->rdev;
 	if (rdev) {
+		if (number >= conf->raid_disks &&
+		    conf->reshape_progress == MaxSector)
+			clear_bit(In_sync, &rdev->flags);
+
 		if (test_bit(In_sync, &rdev->flags) ||
 		    atomic_read(&rdev->nr_pending)) {
 			err = -EBUSY;
@@ -4657,7 +4667,8 @@ static int raid5_remove_disk(mddev_t *mddev, int number)
 		 * isn't possible.
 		 */
 		if (!test_bit(Faulty, &rdev->flags) &&
-		    mddev->degraded <= conf->max_degraded) {
+		    mddev->degraded <= conf->max_degraded &&
+		    number < conf->raid_disks) {
 			err = -EBUSY;
 			goto abort;
 		}
@@ -4745,16 +4756,26 @@ static int raid5_resize(mddev_t *mddev, sector_t sectors)
 static int raid5_check_reshape(mddev_t *mddev)
 {
 	raid5_conf_t *conf = mddev_to_conf(mddev);
-	int err;
 
-	if (mddev->delta_disks < 0 ||
-	    mddev->new_level != mddev->level)
-		return -EINVAL; /* Cannot shrink array or change level yet */
 	if (mddev->delta_disks == 0)
 		return 0; /* nothing to do */
 	if (mddev->bitmap)
 		/* Cannot grow a bitmap yet */
 		return -EBUSY;
+	if (mddev->degraded > conf->max_degraded)
+		return -EINVAL;
+	if (mddev->delta_disks < 0) {
+		/* We might be able to shrink, but the devices must
+		 * be made bigger first.
+		 * For raid6, 4 is the minimum size.
+		 * Otherwise 2 is the minimum
+		 */
+		int min = 2;
+		if (mddev->level == 6)
+			min = 4;
+		if (mddev->raid_disks + mddev->delta_disks < min)
+			return -EINVAL;
+	}
 
 	/* Can only proceed if there are plenty of stripe_heads.
 	 * We need a minimum of one full stripe,, and for sensible progress
@@ -4771,14 +4792,7 @@ static int raid5_check_reshape(mddev_t *mddev)
 		return -ENOSPC;
 	}
 
-	err = resize_stripes(conf, conf->raid_disks + mddev->delta_disks);
-	if (err)
-		return err;
-
-	if (mddev->degraded > conf->max_degraded)
-		return -EINVAL;
-	/* looks like we might be able to manage this */
-	return 0;
+	return resize_stripes(conf, conf->raid_disks + mddev->delta_disks);
 }
 
 static int raid5_start_reshape(mddev_t *mddev)
@@ -4803,6 +4817,17 @@ static int raid5_start_reshape(mddev_t *mddev)
 		 */
 		return -EINVAL;
 
+	/* Refuse to reduce size of the array.  Any reductions in
+	 * array size must be through explicit setting of array_size
+	 * attribute.
+	 */
+	if (raid5_size(mddev, 0, conf->raid_disks + mddev->delta_disks)
+	    < mddev->array_sectors) {
+		printk(KERN_ERR "md: %s: array size must be reduced "
+		       "before number of disks\n", mdname(mddev));
+		return -EINVAL;
+	}
+
 	atomic_set(&conf->reshape_stripes, 0);
 	spin_lock_irq(&conf->device_lock);
 	conf->previous_raid_disks = conf->raid_disks;
@@ -4836,9 +4861,12 @@ static int raid5_start_reshape(mddev_t *mddev)
 				break;
 		}
 
-	spin_lock_irqsave(&conf->device_lock, flags);
-	mddev->degraded = (conf->raid_disks - conf->previous_raid_disks) - added_devices;
-	spin_unlock_irqrestore(&conf->device_lock, flags);
+	if (mddev->delta_disks > 0) {
+		spin_lock_irqsave(&conf->device_lock, flags);
+		mddev->degraded = (conf->raid_disks - conf->previous_raid_disks)
+			- added_devices;
+		spin_unlock_irqrestore(&conf->device_lock, flags);
+	}
 	mddev->raid_disks = conf->raid_disks;
 	mddev->reshape_position = 0;
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
@@ -4863,6 +4891,9 @@ static int raid5_start_reshape(mddev_t *mddev)
 }
 #endif
 
+/* This is called from the reshape thread and should make any
+ * changes needed in 'conf'
+ */
 static void end_reshape(raid5_conf_t *conf)
 {
 
@@ -4886,25 +4917,44 @@ static void end_reshape(raid5_conf_t *conf)
 	}
 }
 
+/* This is called from the raid5d thread with mddev_lock held.
+ * It makes config changes to the device.
+ */
 static void raid5_finish_reshape(mddev_t *mddev)
 {
 	struct block_device *bdev;
 
 	if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
 
-		md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
-		set_capacity(mddev->gendisk, mddev->array_sectors);
-		mddev->changed = 1;
-		mddev->reshape_position = MaxSector;
+		if (mddev->delta_disks > 0) {
+			md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
+			set_capacity(mddev->gendisk, mddev->array_sectors);
+			mddev->changed = 1;
 
-		bdev = bdget_disk(mddev->gendisk, 0);
-		if (bdev) {
-			mutex_lock(&bdev->bd_inode->i_mutex);
-			i_size_write(bdev->bd_inode,
-				     (loff_t)mddev->array_sectors << 9);
-			mutex_unlock(&bdev->bd_inode->i_mutex);
-			bdput(bdev);
+			bdev = bdget_disk(mddev->gendisk, 0);
+			if (bdev) {
+				mutex_lock(&bdev->bd_inode->i_mutex);
+				i_size_write(bdev->bd_inode,
+					     (loff_t)mddev->array_sectors << 9);
+				mutex_unlock(&bdev->bd_inode->i_mutex);
+				bdput(bdev);
+			}
+		} else {
+			int d;
+			raid5_conf_t *conf = mddev_to_conf(mddev);
+			mddev->degraded = conf->raid_disks;
+			for (d = 0; d < conf->raid_disks ; d++)
+				if (conf->disks[d].rdev &&
+				    test_bit(In_sync,
+					     &conf->disks[d].rdev->flags))
+					mddev->degraded--;
+			for (d = conf->raid_disks ;
+			     d < conf->raid_disks - mddev->delta_disks;
+			     d++)
+				raid5_remove_disk(mddev, d);
 		}
+		mddev->reshape_position = MaxSector;
+		mddev->delta_disks = 0;
 	}
 }