dm snapshot: use merge origin if snapshot invalid

If the snapshot we are merging became invalid (e.g. it ran out of
space) redirect all I/O directly to the origin device.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 4c80e82f941c..ee8eb283650d 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1699,11 +1699,9 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
 
         down_write(&s->lock);
 
-        /* Full snapshots are not usable */
-        if (!s->valid) {
-                r = -EIO;
-                goto out_unlock;
-        }
+        /* Full merging snapshots are redirected to the origin */
+        if (!s->valid)
+                goto redirect_to_origin;
 
         /* If the block is already remapped - use that */
         e = dm_lookup_exception(&s->complete, chunk);
@@ -1726,6 +1724,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
                 goto out_unlock;
         }
 
+redirect_to_origin:
         bio->bi_bdev = s->origin->bdev;
 
         if (bio_rw(bio) == WRITE) {