3.16.83-rc1 review patch. If anyone has any objections, please let me know.
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From: Hou Tao houtao1@huawei.com
commit 474e559567fa631dea8fb8407ab1b6090c903755 upstream.
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.
Signed-off-by: Hou Tao houtao1@huawei.com Acked-by: Joe Thornber ejt@redhat.com Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/md/persistent-data/dm-btree-remove.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- 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 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) { /*