dm btree remove: fix bug in redistribute3

commit 4c7e309340ff85072e96f529582d159002c36734 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/md/persistent-data/dm-btree-remove.c b/drivers/md/persistent-data/dm-btree-remove.c
index 1de0f5f..6e79c11 100644 (file)
--- 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 */
 
                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
                        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);
                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
                        shift(left, right, s);
                        nr_left -= s;
                } else