If dispatching write request to merging snapshot device directly to the origin
(because the chunk is not remapped or was already merged), we must make
exceptions in other snapshots.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-snap.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux-2.6.26-devel/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.26-devel.orig/drivers/md/dm-snap.c	2008-07-14 20:24:03.000000000 +0200
+++ linux-2.6.26-devel/drivers/md/dm-snap.c	2008-07-14 20:24:18.000000000 +0200
@@ -1339,6 +1339,11 @@ static int snapshot_merge_map(struct dm_
 
 	bio->bi_bdev = s->origin->bdev;
 
+	if (bio_rw(bio) == WRITE) {
+		up_write(&s->lock);
+		return do_origin(s->origin, bio);
+	}
+
  out_unlock:
 	up_write(&s->lock);