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authorHou Tao <houtao1@huawei.com>2019-12-03 19:42:58 +0800
committerMike Snitzer <snitzer@redhat.com>2019-12-05 15:27:52 -0500
commit474e559567fa631dea8fb8407ab1b6090c903755 (patch)
treec63e8ab7002b64e30b1895bd67e3164f1bb5ec20 /drivers/md/persistent-data
parent484e0d2b11e1fdd0d17702b282eb2ed56148385f (diff)
dm btree: increase rebalance threshold in __rebalance2()
We got the following warnings from thin_check during thin-pool setup: $ thin_check /dev/vdb examining superblock examining devices tree missing devices: [1, 84] too few entries in btree_node: 41, expected at least 42 (block 138, max_entries = 126) examining mapping tree The phenomenon is the number of entries in one node of details_info tree is less than (max_entries / 3). And it can be easily reproduced by the following procedures: $ new a thin pool $ presume the max entries of details_info tree is 126 $ new 127 thin devices (e.g. 1~127) to make the root node being full and then split $ remove the first 43 (e.g. 1~43) thin devices to make the children reblance repeatedly $ stop the thin pool $ thin_check The root cause is that the B-tree removal procedure in __rebalance2() doesn't guarantee the invariance: the minimal number of entries in non-root node should be >= (max_entries / 3). Simply fix the problem by increasing the rebalance threshold to make sure the number of entries in each child will be greater than or equal to (max_entries / 3 + 1), so no matter which child is used for removal, the number will still be valid. Cc: stable@vger.kernel.org Signed-off-by: Hou Tao <houtao1@huawei.com> Acked-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md/persistent-data')
-rw-r--r--drivers/md/persistent-data/dm-btree-remove.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/drivers/md/persistent-data/dm-btree-remove.c b/drivers/md/persistent-data/dm-btree-remove.c
index 21ea537bd55e..eff04fa23dfa 100644
--- a/drivers/md/persistent-data/dm-btree-remove.c
+++ b/drivers/md/persistent-data/dm-btree-remove.c
@@ -203,7 +203,13 @@ static void __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
struct btree_node *right = r->n;
uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
- unsigned threshold = 2 * merge_threshold(left) + 1;
+ /*
+ * Ensure the number of entries in each child will be greater
+ * than or equal to (max_entries / 3 + 1), so no matter which
+ * child is used for removal, the number will still be not
+ * less than (max_entries / 3).
+ */
+ unsigned int threshold = 2 * (merge_threshold(left) + 1);
if (nr_left + nr_right < threshold) {
/*