[PATCH] md/raid10: reject llbitmap reshape when md chunk shrinks

From: Yu Kuai <[email protected]>

llbitmap reshape keeps one live bitmap and cannot safely make an
existing bitmap bit cover a smaller data range.

The llbitmap chunksize itself will not shrink when mddev->chunk_sectors
stays the same or grows. However, shrinking mddev->chunk_sectors can
shrink the effective data range covered by each bit for the RAID10
reshape geometry. Reject that reshape while llbitmap is active.

Signed-off-by: Yu Kuai <[email protected]>
---
 drivers/md/raid10.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 5bd7698e0a1b..c69ef76c89e1 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4269,10 +4269,14 @@ static int raid10_check_reshape(struct mddev *mddev)
 	struct r10conf *conf = mddev->private;
 	struct geom geo;
 
 	if (conf->geo.far_copies != 1 && !conf->geo.far_offset)
 		return -EINVAL;
+	if (mddev->bitmap_id == ID_LLBITMAP &&
+	    mddev->new_chunk_sectors &&
+	    mddev->new_chunk_sectors < mddev->chunk_sectors)
+		return -EOPNOTSUPP;
 
 	if (setup_geo(&geo, mddev, geo_start) != conf->copies)
 		/* mustn't change number of copies */
 		return -EINVAL;
 	if (geo.far_copies > 1 && !geo.far_offset)
-- 
2.51.0