dm btree remove: fix bug in redistribute3

redistribute3() shares entries out across 3 nodes.  Some entries were
being moved the wrong way, breaking the ordering.  This manifested as a
BUG() in dm-btree-remove.c:shift() when entries were removed from the
btree.

For additional context see:
https://www.redhat.com/archives/dm-devel/2015-May/msg00113.html

Signed-off-by: Dennis Yang <shinrairis@gmail.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/md/persistent-data/dm-btree-remove.c b/drivers/md/persistent-data/dm-btree-remove.c
index e04cfd2d60ef..9836c0ae897c 100644
--- a/drivers/md/persistent-data/dm-btree-remove.c
+++ b/drivers/md/persistent-data/dm-btree-remove.c
@@ -309,8 +309,8 @@ static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
 
                 if (s < 0 && nr_center < -s) {
                         /* not enough in central node */
-                        shift(left, center, nr_center);
-                        s = nr_center - target;
+                        shift(left, center, -nr_center);
+                        s += nr_center;
                         shift(left, right, s);
                         nr_right += s;
                 } else
@@ -323,7 +323,7 @@ static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
                 if (s > 0 && nr_center < s) {
                         /* not enough in central node */
                         shift(center, right, nr_center);
-                        s = target - nr_center;
+                        s -= nr_center;
                         shift(left, right, s);
                         nr_left -= s;
                 } else