md/raid5: reshape using largest of old and new chunk size

This ensures that even when old and new stripes are overlapping,
we will try to read all of the old before having to write any
of the new.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid5.c

@@ -3738,6 +3738,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 	int dd_idx;
 	sector_t writepos, safepos, gap;
 	sector_t stripe_addr;
+	int reshape_sectors;
 
 	if (sector_nr == 0) {
 		/* If restarting in the middle, skip the initial sectors */
@@ -3755,6 +3756,15 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 		}
 	}
 
+	/* We need to process a full chunk at a time.
+	 * If old and new chunk sizes differ, we need to process the
+	 * largest of these
+	 */
+	if (mddev->new_chunk > mddev->chunk_size)
+		reshape_sectors = mddev->new_chunk / 512;
+	else
+		reshape_sectors = mddev->chunk_size / 512;
+
 	/* we update the metadata when there is more than 3Meg
 	 * in the block range (that is rather arbitrary, should
 	 * probably be time based) or when the data about to be
@@ -3768,12 +3778,12 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 	safepos = conf->reshape_safe;
 	sector_div(safepos, data_disks);
 	if (mddev->delta_disks < 0) {
-		writepos -= conf->chunk_size/512;
-		safepos += conf->chunk_size/512;
+		writepos -= reshape_sectors;
+		safepos += reshape_sectors;
 		gap = conf->reshape_safe - conf->reshape_progress;
 	} else {
-		writepos += conf->chunk_size/512;
-		safepos -= conf->chunk_size/512;
+		writepos += reshape_sectors;
+		safepos -= reshape_sectors;
 		gap = conf->reshape_progress - conf->reshape_safe;
 	}
 
@@ -3799,14 +3809,14 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 		BUG_ON(conf->reshape_progress == 0);
 		stripe_addr = writepos;
 		BUG_ON((mddev->dev_sectors &
-			~((sector_t)conf->chunk_size / 512 - 1))
-		       - (conf->chunk_size / 512) - stripe_addr
+			~((sector_t)reshape_sectors - 1))
+		       - reshape_sectors - stripe_addr
 		       != sector_nr);
 	} else {
-		BUG_ON(writepos != sector_nr + conf->chunk_size / 512);
+		BUG_ON(writepos != sector_nr + reshape_sectors);
 		stripe_addr = sector_nr;
 	}
-	for (i=0; i < conf->chunk_size/512; i+= STRIPE_SECTORS) {
+	for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
 		int j;
 		int skipped = 0;
 		sh = get_active_stripe(conf, stripe_addr+i, 0, 0);
@@ -3839,9 +3849,9 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 	}
 	spin_lock_irq(&conf->device_lock);
 	if (mddev->delta_disks < 0)
-		conf->reshape_progress -= i * new_data_disks;
+		conf->reshape_progress -= reshape_sectors * new_data_disks;
 	else
-		conf->reshape_progress += i * new_data_disks;
+		conf->reshape_progress += reshape_sectors * new_data_disks;
 	spin_unlock_irq(&conf->device_lock);
 	/* Ok, those stripe are ready. We can start scheduling
 	 * reads on the source stripes.
@@ -3867,7 +3877,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 	/* If this takes us to the resync_max point where we have to pause,
 	 * then we need to write out the superblock.
 	 */
-	sector_nr += conf->chunk_size>>9;
+	sector_nr += reshape_sectors;
 	if (sector_nr >= mddev->resync_max) {
 		/* Cannot proceed until we've updated the superblock... */
 		wait_event(conf->wait_for_overlap,
@@ -3883,7 +3893,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
 		spin_unlock_irq(&conf->device_lock);
 		wake_up(&conf->wait_for_overlap);
 	}
-	return conf->chunk_size>>9;
+	return reshape_sectors;
 }
 
 /* FIXME go_faster isn't used */