[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <ba7c09b103a4580e23b961c3e2541a54272c8edf.1448283890.git.jslaby@suse.cz>
Date: Mon, 23 Nov 2015 14:07:04 +0100
From: Jiri Slaby <jslaby@...e.cz>
To: stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Joe Thornber <ejt@...hat.com>,
Mike Snitzer <snitzer@...hat.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 01/72] dm btree remove: fix a bug when rebalancing nodes after removal
From: Joe Thornber <ejt@...hat.com>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit 2871c69e025e8bc507651d5a9cf81a8a7da9d24b upstream.
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@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
drivers/md/persistent-data/dm-btree-remove.c | 17 +++++++++++------
1 file 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 7c0d75547ccf..92cd09f3c69b 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];
--
2.6.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists