Commit 4c7e309340 ("dm btree remove: fix bug in redistribute3") wasn't
a complete fix for redistribute3().
The redistribute3 function takes 3 btree nodes and shares out the entries
evenly between them. If the three nodes in total contained
(MAX_ENTRIES * 3) - 1 entries between them then this was erroneously getting
rebalanced as (MAX_ENTRIES - 1) on the left and right, and (MAX_ENTRIES + 1) in
the center.
Fix this issue by being more careful about calculating the target number
of entries for the left and right nodes.
Unit tested in userspace using this program:
https://github.com/jthornber/redistribute3-test/blob/master/redistribute3_t.c
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
2871c69e02