[PATCH] ubi: Make volume resize power cut aware

[Richard Weinberger]

When the volume resize operation shrinks a volume,
LEBs will be unmapped. Since unmapping will not erase these
LEBs immediately we have to wait for that operation to finish.
Otherwise in case of a power cut right after writing the new
volume table the UBI attach process can find more LEBs than the
volume table knows. This will render the UBI image unattachable.

Fix this issue by waiting for erase to complete and write the new volume table afterward.

Cc: <stable at vger.kernel.org>
Reported-by: Boris Brezillon <boris.brezillon at free-electrons.com>
Signed-off-by: Richard Weinberger <richard at nod.at>
---
 drivers/mtd/ubi/vmt.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
index 10059df..0138f52 100644
--- a/drivers/mtd/ubi/vmt.c
+++ b/drivers/mtd/ubi/vmt.c
@@ -488,13 +488,6 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
 		spin_unlock(&ubi->volumes_lock);
 	}
 
-	/* Change volume table record */
-	vtbl_rec = ubi->vtbl[vol_id];
-	vtbl_rec.reserved_pebs = cpu_to_be32(reserved_pebs);
-	err = ubi_change_vtbl_record(ubi, vol_id, &vtbl_rec);
-	if (err)
-		goto out_acc;
-
 	if (pebs < 0) {
 		for (i = 0; i < -pebs; i++) {
 			err = ubi_eba_unmap_leb(ubi, vol, reserved_pebs + i);
@@ -512,6 +505,24 @@ int ubi_resize_volume(struct ubi_volume_desc *desc, int reserved_pebs)
 		spin_unlock(&ubi->volumes_lock);
 	}
 
+	/*
+	 * When we shrink a volume we have to flush all pending (erase) work.
+	 * Otherwise it can happen that upon next attach UBI finds a LEB with
+	 * lnum > highest_lnum and refuses to attach.
+	 */
+	if (pebs < 0) {
+		err = ubi_wl_flush(ubi, vol_id, UBI_ALL);
+		if (err)
+			goto out_acc;
+	}
+
+	/* Change volume table record */
+	vtbl_rec = ubi->vtbl[vol_id];
+	vtbl_rec.reserved_pebs = cpu_to_be32(reserved_pebs);
+	err = ubi_change_vtbl_record(ubi, vol_id, &vtbl_rec);
+	if (err)
+		goto out_acc;
+
 	vol->reserved_pebs = reserved_pebs;
 	if (vol->vol_type == UBI_DYNAMIC_VOLUME) {
 		vol->used_ebs = reserved_pebs;
-- 
2.7.3