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| author | Joe Thornber <ejt@redhat.com> | 2015-10-21 18:36:49 +0100 |
|---|---|---|
| committer | Mike Snitzer <snitzer@redhat.com> | 2015-10-23 14:02:55 -0400 |
| commit | 2871c69e025e8bc507651d5a9cf81a8a7da9d24b (patch) | |
| tree | e1101ed40df4065187db2cde572f449ff708bb67 /drivers/md | |
| parent | ba30670f4d5292c4e7f7980bbd5071f7c4794cdd (diff) | |
| download | linux-2871c69e025e8bc507651d5a9cf81a8a7da9d24b.tar.gz linux-2871c69e025e8bc507651d5a9cf81a8a7da9d24b.tar.bz2 linux-2871c69e025e8bc507651d5a9cf81a8a7da9d24b.zip | |
dm btree remove: fix a bug when rebalancing nodes after removal
Commit 4c7e309340ff ("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
Diffstat (limited to 'drivers/md')
| -rw-r--r-- | drivers/md/persistent-data/dm-btree-remove.c | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/drivers/md/persistent-data/dm-btree-remove.c b/drivers/md/persistent-data/dm-btree-remove.c index 421a36c593e3..2e4c4cb79e4d 100644 --- a/drivers/md/persistent-data/dm-btree-remove.c +++ b/drivers/md/persistent-data/dm-btree-remove.c @@ -301,11 +301,16 @@ static void redistribute3(struct dm_btree_info *info, struct btree_node *parent, { int s; uint32_t max_entries = le32_to_cpu(left->header.max_entries); - unsigned target = (nr_left + nr_center + nr_right) / 3; - BUG_ON(target > max_entries); + unsigned total = nr_left + nr_center + nr_right; + unsigned target_right = total / 3; + unsigned remainder = (target_right * 3) != total; + unsigned target_left = target_right + remainder; + + BUG_ON(target_left > max_entries); + BUG_ON(target_right > max_entries); if (nr_left < nr_right) { - s = nr_left - target; + s = nr_left - target_left; if (s < 0 && nr_center < -s) { /* not enough in central node */ @@ -316,10 +321,10 @@ static void redistribute3(struct dm_btree_info *info, struct btree_node *parent, } else shift(left, center, s); - shift(center, right, target - nr_right); + shift(center, right, target_right - nr_right); } else { - s = target - nr_right; + s = target_right - nr_right; if (s > 0 && nr_center < s) { /* not enough in central node */ shift(center, right, nr_center); @@ -329,7 +334,7 @@ static void redistribute3(struct dm_btree_info *info, struct btree_node *parent, } else shift(center, right, s); - shift(left, center, nr_left - target); + shift(left, center, nr_left - target_left); } *key_ptr(parent, c->index) = center->keys[0]; |