Btrfs: update free_chunk_space during allocting a new chunk

We should update free_chunk_space in time when we allocate a new chunk,
not when we deal with the pending device update and block group insertion,
because we need the real free_chunk_space data to calculate the reserved
space, if we don't update it in time, we would consider the disk space which
has be allocated as free space, and would use it to do overcommit reservation.
Fix it.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/volumes.c

@@ -4432,6 +4432,11 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	for (i = 0; i < map->num_stripes; i++)
 		map->stripes[i].dev->bytes_used += stripe_size;
 
+	spin_lock(&extent_root->fs_info->free_chunk_lock);
+	extent_root->fs_info->free_chunk_space -= (stripe_size *
+						   map->num_stripes);
+	spin_unlock(&extent_root->fs_info->free_chunk_lock);
+
 	free_extent_map(em);
 	check_raid56_incompat_flag(extent_root->fs_info, type);
 
@@ -4515,11 +4520,6 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 			goto out;
 	}
 
-	spin_lock(&extent_root->fs_info->free_chunk_lock);
-	extent_root->fs_info->free_chunk_space -= (stripe_size *
-						   map->num_stripes);
-	spin_unlock(&extent_root->fs_info->free_chunk_lock);
-
 	stripe = &chunk->stripe;
 	for (i = 0; i < map->num_stripes; i++) {
 		device = map->stripes[i].dev;