Btrfs: fix the number of transaction units needed to remove a block group

[cascardo/linux.git] / fs / btrfs / extent-tree.c

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7820093..e97d6d6 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10257,14 +10257,44 @@ out:
 }
 
 struct btrfs_trans_handle *
-btrfs_start_trans_remove_block_group(struct btrfs_fs_info *fs_info)
+btrfs_start_trans_remove_block_group(struct btrfs_fs_info *fs_info,
+                                    const u64 chunk_offset)
 {
+       struct extent_map_tree *em_tree = &fs_info->mapping_tree.map_tree;
+       struct extent_map *em;
+       struct map_lookup *map;
+       unsigned int num_items;
+
+       read_lock(&em_tree->lock);
+       em = lookup_extent_mapping(em_tree, chunk_offset, 1);
+       read_unlock(&em_tree->lock);
+       ASSERT(em && em->start == chunk_offset);
+
        /*
+        * We need to reserve 3 + N units from the metadata space info in order
+        * to remove a block group (done at btrfs_remove_chunk() and at
+        * btrfs_remove_block_group()), which are used for:
+        *
         * 1 unit for adding the free space inode's orphan (located in the tree
         * of tree roots).
+        * 1 unit for deleting the block group item (located in the extent
+        * tree).
+        * 1 unit for deleting the free space item (located in tree of tree
+        * roots).
+        * N units for deleting N device extent items corresponding to each
+        * stripe (located in the device tree).
+        *
+        * In order to remove a block group we also need to reserve units in the
+        * system space info in order to update the chunk tree (update one or
+        * more device items and remove one chunk item), but this is done at
+        * btrfs_remove_chunk() through a call to check_system_chunk().
         */
+       map = (struct map_lookup *)em->bdev;
+       num_items = 3 + map->num_stripes;
+       free_extent_map(em);
+
        return btrfs_start_transaction_fallback_global_rsv(fs_info->extent_root,
-                                                          1, 1);
+                                                          num_items, 1);
 }
 
 /*
@@ -10333,7 +10363,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
                 * Want to do this before we do anything else so we can recover
                 * properly if we fail to join the transaction.
                 */
-               trans = btrfs_start_trans_remove_block_group(fs_info);
+               trans = btrfs_start_trans_remove_block_group(fs_info,
+                                                    block_group->key.objectid);
                if (IS_ERR(trans)) {
                        btrfs_dec_block_group_ro(root, block_group);
                        ret = PTR_ERR(trans);